Cook rice according to package instructions. In small bowl, mix chili powder, cumin, salt & cayenne (optional). Place fish in shallow dish and sprinkle both sides with spice mixture. In large skillet, heat oil on med and cook garlic for 1-2 mins, stirring constantly. Add fish and cook approx 10 mins, turning over during cooking, until opaque and flakes easily- it's ok if fish breaks up into pieces during cooking. Remove fish from pan and set aside. Add corn, onion, & pepper to skillet and cook until tender, about 5 mins. Stir in beans and heat until just warmed. Divide rice, fish, and corn/pepper/onion mixture between bowls. Squeeze lime wedges over top of bowls and top with chopped cilantro, if using.