Dice the onions and stew in the hot oil until they turn brown. Then add the diced meat and cook for about 5 minutes over a low heat, stirring constantly. Season with salt.
Then add the curry paste to the meat, stir and pour in the water and coconut milk. Add the diced tomatoes and let the whole thing simmer for about 1 - 2 hours on a low flame, so that the meat becomes nice and soft. Possibly season the sauce with a little salt and the spices.
If the sauce is still too runny at the end of the cooking time, then thicken the sauce with a little flour.
Basmati rice can be served with it.
Note: If you choose a different type of meat, you must of course adjust or shorten the cooking time accordingly!