Heat the oil in a large iron skillet or a Dutch oven over moderately high heat.
Season the chicken thighs or legs with salt and pepper, and cook until all sides of the chicken turn brown, about five minutes. Remove the chicken from the skillet and set aside.
In the meantime, finely chop the onion and slice the olives.
Cook onions: Reduce the heat and add the finely chopped onion. Cook for about three minutes or until it becomes soft and translucent.
Add sofrito, capers, sliced olives, and tomato sauce to the skillet and cook for 5 minutes.
Add the washed and drained rice, chicken, and water to the pan. Increase the heat slightly and bring the water to a gentle boil. Cook without a lid on high heat until most of the stock has boiled off.
Simmer: Add the peas and stir the rice gently. Cover the pot very tightly, reduce the heat to low, and continue cooking on low heat for about 20 minutes or until the rice is done. Serve immediately.
Notes
Sofrito is a blend of vegetables, like onions, garlic, tomatoes peppers, cooked with herbs and spices. It is used to flavor rice, beans, stews, and many other dishes.