In a deep skillet, cook 3/4 cup onion, chopped and 2 cloves garlic, minced in 1 tsp olive oil on medium heat for a few minutes until soft. Add 2 1/2 cups tomatoes, chopped, 3/4 cup diced sweet peppers and 1 tbsp Cajun spice seasoning, stir and cook until tomatoes are soft, about 2-3 minutes. Lay 4 (6 oz) pieces fish in the sauce, cover and cook on medium-low until fish flakes easily, approx 12-15. To serve, place fish on plate and spoon sauce on top. Serve immediately over white rice.