Combine the olive oil and lime juice with the tuna steaks and set aside to marinate for 30 minutes.
Combine all the ingredients for the mango salsa. Season with salt and pepper to taste. Prepare it 30 minutes prior to serving for best flavor.
Heat a cast iron grill on high heat until hot. Lightly oil the grill and season both sides of the tuna steaks with salt and pepper. Grill each side for 2-3 minutes. Let the tuna rest for 10-15 minutes before serving.