Any methods to make prawns more "crunchy" (bite/tear off easily)
Chewy or rubbery prawns are a good sign that you've overcooked them. As with other seafood, they don't take kindly to being overcooked. You should probably cook them separately, just enough, and then mix them into whatever you're eating them with.

You can use whatever cooking method you like; common ones include boiling, steaming, and stir-frying. Whatever you do, just make sure you don't do too much of it. Any cooking beyond done makes them worse.

Since you seem to prefer boiling: as soon as they're done, you should dump them into a colander and run cold water over them immediately afterward to stop them from cooking further. Cooking times vary depending on size; small shrimp take only a few minutes, while very large ones might take 5-10. They'll probably be pink and some will be starting to float; to tell for sure whether they're cooked you can cut one in half and make sure it's opaque all the way through.