Halve the avocado, remove the stone, peel off the skin and dice into small pieces. Transfer them to a bowl and place all the remaining ingredients, cherry tomatoes, mango, lime juice, olive oil and finally season with salt and pepper and place the bowl in the refrigerator for 30 minutes before serving, this will help the flavors to develop.
Meanwhile heat a griddle pan or barbeque until hot. Brush the tuna steaks with olive oil on both sides and season with salt and pepper. Cook on the grill for 1 to 2 minutes on each side for medium or cook to your liking.
When tuna are ready transfer them onto warm serving plates and pour over the mixture.