In a large resealable plastic bag, mix 2 tablespoons sesame oil, the chopped garlic, 1/4 teaspoon black pepper, and the soy sauce. Add tuna steaks to bag, seal, and marinate in the refrigerator for 60 minutes.
Meanwhile, in a small bowl, mix sesame seeds, bread crumbs, ground ginger, the remaining black pepper and remaining sesame oil.
Preheat oven to 400°F. Coat a rimmed baking sheet with nonstick cooking spray. Remove tuna from marinade, discard marinade, and place tuna steaks on baking sheet. Top evenly with sesame seed mixture and bake 12 to 15 minutes.
