How to dice tomatoes?

Cut the tomato in half at the midsection or equator (stem end being the "north pole") to expose the seed cavities. Holding the cut side down over your garbage bowl or trash can, gently squeeze to remove the seeds. You can easily pry out stubborn seeds with your fingertips.

Place the tomato half cut-side up on the cutting board (Cutting waxy skinned vegetables is much easier when the skin is on the bottom so the force of the knive cuts cleanly through the skin with less effot) and cut in half again. After doing this with both pieces the tomato will be in quarters.

If you want evenly diced pieces of just the exterior flesh (such as for sprinkling on a plate for a garnish), then use your knife to cut out the interior portion so that just the tomato "shell" remains. You can then easily dice the exterior shell.

Otherwise, after cutting into quarters just gently push down to flatten each quarter and cut into strips lengthwise and then cut cross-wise to finish the process.

While cumbersome to explain in text, it's much safer and quicker than cutting the tomato into slices and then trying to dice from there.

What is it with tomatoes and their seeds? As Papin says, the "pulp" which is inside a tomato adds "umami" taste to dishes, or at least a good taste.

Why would anyone using tomatoes wish to remove the best tasting parts of the veg?

I find the peel and de-seed tomatoes to be time-consuming and wasteful of the good parts of the tomato and my time, which I don't have that much of.

I slice tomatoes however thin one way, then across the disks the first cut produces that same thickness, and then across the sticks the second cut produces, using a big cutting board and a big sharp knife. You get little cubes of the firmer parts and assorted seeds and pulp along with. I drain some moisture if the dish won't benefit from it, which is rare.

What I've been doing lately for large batches is using a food processor or blender. Specifically I've been using a Ninja blender that was about $70.

I cut the tops off the tomatoes and sometimes cut them into a few large chunks and put them in the blender. I use the pulse function to slowly get them to the consistency that I want. If you just go full blend you'll get more of a tomato sauce consistency.

Afterwards they will still have a bit of air in them. It makes them look like someone chewed them up and spit them out with all the bubbles. If you have the time, you can just let them sit for a while and the bubbles will take care of themselves.

It's not quite as nice presentation wise as hand dicing, and I can't get the chunks as fine as I would do it by hand, but it IS significantly faster. It's a decent compromise that works for me.

I'll also usually do most of the other ingredients this way as well - onions, peppers, cilantro - but I always do the tomatoes separately and then combine afterwards.

Cut enough off the top to expose the seeds. Cut enough off the botton to expose the seeds. Now you have a barrel shaped bit of tomato.

Place, the tomato on it's side, so that one of the flat sides is facing you. Now cut half way through the tomato such that the thickness of the slice is about the thickness of the tomato wall. Rather than cutting all the way through, start turning your knife so that you cut out the core of the tomato.

You now have a large rectangle piece of tomato and dicing is easy.

A different method, requires a little practise, but quick & easy once you have it. This method keeps the seeds, but loses the harder green bit where the stalk was attached.

This is the quickest manual method I have ever seen & produces evenly sized chunks - it takes considerably longer to explain than to do. It requires a razor-sharp knife, otherwise you tend to just push the tomato out of your grip & lose control of it.

Place the tomato stalk side down, for initial stability*.
Make an even number of vertical cuts, parallel to each other - so you get 3, 5 or 7 equal-thickness slices, depending on tomato size & required chunk size. Don't let go, keep the tomato complete in your hand.
Now it gets trickier, because you have to constantly keep hold...
All horizontal cuts are only half way. All vertical cuts are right through to your board.
You no longer need to count how many cuts for the rest of the task.
Make several horizontal cuts at 90° to your first ones, parallel to your chopping board - but only half way through. It's more stable if you start at the bottom & work upwards. (Yes, you are cutting towards your own hand - be careful)
Slice again a couple of times vertically, at 90° to both existing cut directions, until you reach about halfway (all these 'halfways' become clear by the end) - & off come your first few chunks; slide to one side with your knife.
Rotate the remainder onto the flat face.
Make similar horizontal & vertical cuts; freeing your second set of pieces.
Rotate the remainder again, onto the face you just cut.
Depending on the tomato size, you may have room for one last horizontal cut, then make a last set of vertical cuts.
Done.
If you got the first counted cuts just right, your 'stalk' piece is separate & ready to discard.

* I've tried this both ways up, as it always feels as though being able to see the stalk when making the first cuts would be better - it isn't, you lose stability & are likely to lose control of the tomato half way through.

One hassle saving method, IF you can afford to waste (or use elsewhere) a bit of tomato in cases where you can ONLY use perfect dice, is to cut it in half, lay the halves then score but NOT CUT FULLY THROUGH the tomato in a dice pattern, then slice off layers of dice with board parallel cuts. If you are dicing to stew the tomatoes, you can usually (if you removed the really hard stem parts before) just take the finely scored half of tomato and throw it in the pan whole - it will stew apart very quickly.

(Note: this method was posted before, paraphrased, by someone else, but then self-deleted).