Samantha's African Peanut Butter Chicken Recipe

I got this recipe from my sister Samantha, and now I think I make it more than she does. It's so good and so simple.

Ingredients:
2 chicken breasts
1 diced onion
4 cloves of garlic
1 tbsp of cumin
1/4 tsp cayenne pepper
1 tsp of chili flakes (approx.)
2 cups of water
1 can of diced tomatoes
about 1 cup of peanut butter
salt & pepper to taste

Cut the chicken into cubes, season with salt and pepper. Put the chicken into a large pot heated to medium. Once the chicken is cooked on all sides, throw in the onions. Once the onions are translucent, add the garlic, cumin, cayenne, and chilies. After about a minute put in the 2 cups of water. Put the heat down to low and simmer for 5 minutes.  You can use chicken stalk instead of water for a more concentrated flavor, I know my sister does, but the water will also turn into chicken stalk after simmering in the chicken.
Add the can of diced tomatoes, simmer again for another 10 minutes or so.
Add the peanut butter, stir well, the sauce should be thick and creamy...if it's not thick enough add more peanut butter. Simmer again for 5 minutes. Season to taste with salt & pepper, maybe add more chilies or cayenne if it needs it (the peanut butter takes away a lot of the spice).
Serve over rice.