Step 1 Rub all sides of tuna steaks with sesame oil and sprinkle with salt. Cover and let stand while preparing cucumber salsa.
Step 2 Combine onions, cucumber, grapefruit, cilantro, Thai pepper, garlic, lime juice, olive oil and 1/2 teaspoon salt. Let stand while grilling tuna.
Step 3Grill tuna steaks over high heat in stove top grill pan or on barbecue grill 5 minutes. Turn and cook until desired doneness, 2 to 5 minutes. Remove tuna to serving platter and serve Cucumber and Grapefruit salsa alongside.