How to prevent minced chicken from sticking and forming a single lump?

The water method works (it keeps the pan from getting above 100°C), but the more generic solution is just to cook it over lower heat, and keep it moving around as it's cooking. (and this works for any ground meat product).

If you let one lump brown too much and form a crust, it'll fuse that bit together. You then need to break up that bit (I like a spatulas, so just flip over the lump so the browned side is up, and then either squish it or chop at it 'til it's broken down to a smaller size. Reducing the heat while you're cooking will give you more time to break up lumps before they've fused together.

I generally turn the stove to medium heat, and then add the meat before it's fully pre-heated. I give it a couple of seconds to brown, then flip the whole blob over and break it up so it's spread throughout the pan ... wait a bit for the bottom to brown again, and then continue flipping and breaking it up.

If you're going to be standing right over the dish, you can use a higher heat, but I generally tend to be doing something else nearby (eg, chopping vegetables) while this is going on, so adjust the heat so it's cooking at a rate where I can get back to it easily.

If you're going to be adding some other chunky item to the minced meat (eg, chopped onion) that won't be impacted from extra cooking time, go ahead and add it after the meat's only partially cooked, as the meat won't stick as well to it as it would to other meat, making it less likely to clump up (or at least easier to break apart should it clump up)

While the chicken is still cold, add a bit of water (perhaps about 1/4 cup, 125ml per pound of meat). Use your fastidiously clean fingers to break up the chicken pieces in the water. Put it on the flame and stir while the water evaporates. After the water is gone, continue to stir while the chicken browns.

Add a little oil to your pan then add the minced chicken. Using a wooden fork break it up into large chunks and let them cook a little turning them so to firm them up, you can now start breaking the large chunks up into smaller pieces. They wont stick to each other because they should be almost cooked. Continue the process until all the chicken is cooked through and is in small pieces.

This will also mean your chicken retains it's flavour and texture.

Adding water will give you a rather sludgy concoction!

If you want the mince even finer, you could use a stick blender or a food processor AFTER you have done the above.