Heat the oil in a large, heavy skillet over medium-heat heat; cook the chicken in the skillet until completely brown, 5 to 7 minutes; remove and set aside. Add the onion, potatoes, garlic, pepper, salt, coriander, cumin, and red pepper to the skillet and cook until the onions soften, about 5 minutes. Stir in the water, chicken broth, and peanut butter. Return the chicken to the skillet and top with the spinach. Cover and simmer until the potatoes are cooked through, about 20 minutes.