Season the flounder fillets with lemon pepper.
In bowl combine tomato, onion, peppers, mango, cilantro, olive oil, lime juice and black pepper.
Place a half fillet in centre of aluminum foil (cut into 8-12 inch/20-30 cm squares). Top with 1/4 of the tomato and mango mixture. Cover with second half piece of fish. Fold aluminum foil edges together to form a sealed pouch. Repeat for other 3 portions.
Preheat oven to 375°F/190°C. Place foil pouches on baking sheet and bake for 20-25 minutes or until fish becomes flaky.
Remove from oven, allow to rest for 3-4 minutes.
Carefully unwrap the pouch and allow the steam to escape.