1) Heat the oil in a large skillet or heavy pot, then saute onions and pepper together. 2) Mash or grind the tomatoes and stir them in, along with the remaining ingredients. Cook at a moderate temperature for 15 minutes, or until fish is tender and flaky. 3) If there is too much oil on the surface for your liking, skim some off with a spoon. Serve kentumere with cooked plaintain or rice.