Preheat the Grill: Heat your grill to medium-high heat, ensuring the grates are clean and lightly oiled.
Prepare the Tuna: In a small bowl, mix the olive oil, soy sauce, lemon juice, garlic, and any optional ingredients (sesame oil or honey). Season the tuna steaks with salt and pepper. Brush the mixture over the tuna steaks, allowing them to marinate for 15-30 minutes.
Grill the Tuna: Once the grill is ready, place the tuna steaks on the grill. Grill each side for 1-2 minutes for rare, or longer if you prefer more done tuna. Rotate the steaks halfway through cooking to achieve crosshatch grill marks.
Rest and Slice: Once cooked to your desired doneness, remove the tuna from the grill and let it rest for a couple of minutes. Slice the tuna against the grain before serving.
Serve: Serve the grilled ahi tuna with your favorite sides or drizzle with a light dipping sauce like soy sauce or lemon garlic aioli.