In a non-aluminum bowl, combine 3 hot red chilli peppers (finely chopped), half the coriander (chopped), 2 tablespoons garlic (finely chopped), 1 tablespoon paprika powder, 1 tablespoon freshly ground pepper, 125 ml olive oil, and 60 ml lemon juice (freshly squeezed). Place the 750 g tuna (cut into 4 equal slices) in the marinade and rub thoroughly to coat. Cover and refrigerate for 2 hours.
Preheat a charcoal grill to medium-high heat, or preheat an oven grill to 220°C (425°F).
Remove the tuna from the marinade and season with salt. Place on a grate brushed with oil or in a grill pan. Grill for 3 minutes per side for medium doneness, or longer if preferred.
Transfer the tuna to a preheated platter or individual plates, garnish with the remaining coriander, and serve immediately.