How (much) can I minimise the cooking time of red split lentils?

I can’t give you numbers as I haven’t experimented with it yet (but am very inspired to do so by your post), but assuming that you will be heating water for a morning coffee or so, have you considered putting the lentils into a smallish thermos container, topping them up with boiling water and letting them soak / slow cook during the day? Adding your dehydrated veggies and spices wouldn’t require any serious cooking at all, just a quick reheating or bringing it back to a boil.

The idea is roughly based on the principle of a haybox, where food is cooked by placing the hot out into an insulating environment. And combined with the “quick soak” method for beans, where the beans are not soaked in cold, but boiling water, but for just thirty minutes instead of overnight.

Admittedly, this would probably get the lentils in the danger zone for longer than the canonical two hours, but on the other hand, we are not dealing with proteins like meat, raw eggs or dairy. But you could always adjust the time when you start the lentils to fit stricter food safety guidelines or your personal risk tolerance, e.g. boiling the water at your lunch break.

1. Cooking then in unsalted water
2. Pressure cooking - saves 50%-60% of time
3. Soaking them for 2-3 hours and cooking

Generally, I find red split lentils are the easiest ones to cook and they cook in a very short time than any lentils. Yellow split peas take longer to cook.

I'm skeptical about whether adding/omiting salt makes a difference, but it may. Also experiment with adding a little baking soda; pH affects cooking time (and the final consistency), and 'neutral' isn't the limit of the usable range.

I haven't found any really reputable sources on my own, but this excellent answer discusses the role of baking soda in detail: https://cooking.stackexchange.com/a/45012/74018

Finally, take whatever steps you can to get "fresher" dried legumes. I've personally experienced 2x variation in cooking time just with stuff that was hiding at the back of my pantry for too long.

A frame challenge answer: Instead of processing your own lentils, you might look into preprocessed products with reduced cook time.

Right now, my pantry contains two products that might be interesting for your case. One is a red lentil pasta that has a cooktime of 6 minutes, it's possible that other shapes have even quicker cooktimes. Another is chickpea instant couscous - it only requires you to pour boiling water over it and let it sit at room temperature. I haven't seen red lentil couscous, but it wouldn't hurt to look around for this kind of product (or directly base your meal on the chickpea couscous).

If you insist on making your own, you might look into parboiling your lentils instead of presoaking them. This will likely reduce your cooktime a lot, at least it does so with other food like rice. I haven't done it myself, so I can't get you an estimate, but it is likely that significant time savings lie in that direction.

CW as it gathers up some comments, mainly under rumtscho's answer, which started me in the right direction and which I commend.

As it turned out, what worked best was fully cooking them (as dhal), then dehydrating in a low oven (I have a dehydrator but wasn't confident it would maintain >60°C in all areas). The drying dhal needed turning a couple of times, then crumbling, to ensure it dried evenly. I started a little too hot, but a bit of toasting round the edges of the tray did no harm.

A bolognese-like sauce would work similarly, so long as any other ingredients (veg) were finely chopped, and I see no reason why plain fully cooked lentils couldn't be mixed with other ingredients in the field.

The only downside was a slight lack of texture, partly because I'd slow-cooked the dhal in the first place, and partly from the crumbling. In fact as the rice I'd also cooked and dehydrated was reluctant to soften, it had more bite than the dhal, but I still had a ncie hot meal bike-camping with minimal weight and mess.