Finely dice one ripe mango, a quarter of a red onion, and a handful of cherry tomatoes. In a medium bowl, combine with chopped cilantro, lime juice, olive oil, salt, pepper, and optional chili flakes. Toss gently.

Brush both sides of the tuna steaks with olive oil. Season with salt and pepper. Set aside to absorb seasoning.

Preheat grill to medium-high heat, about 400°F (200°C). Place seasoned tuna steaks on the grill and cook for 2-3 minutes on each side.

Transfer grilled tuna steaks onto serving plates and top each with mango salsa. Garnish with lime wedges or additional cilantro.