Light a grill. In a food processor, coarsely chop the almonds, bread cubes and garlic. Add the tomatoes, roasted red peppers, sherry vinegar and pimentón and puree until smooth. With the machine on, gradually add the oil. Season with salt and pepper.
Season the tuna with salt and pepper. Grill over moderate heat, turning once, for 6 minutes for medium-rare, or 8 minutes for medium. Transfer the tuna to plates. Spoon some of the romesco sauce over the fish and pass the rest at the table.