1In a small bowl, combine the olive oil, soy sauce, lime juice, chili powder, cayenne pepper, black pepper, and salt.
Place the tuna steaks in a shallow dish and pour the marinade over them. Turn the steaks to coat them evenly. Cover and refrigerate for at least 30 minutes.
Preheat the grill to high heat.
Lightly oil the grill grate. Remove the tuna steaks from the marinade and discard the marinade.
Grill the tuna steaks for 3 to 4 minutes on each side, or until the desired level of doneness is reached.
Remove from the grill and let rest for a few minutes before serving.
Serve the spicy grilled tuna steaks with your choice of side dishes.