Make the marinade by mixing soy sauce, olive oil, lemon juice, sesame oil, molasses, cayenne pepper, ginger, and garlic together in a bowl.

Place tuna steaks in a large resealable plastic bag or airtight container; pour marinade over steaks, coat with marinade, and seal. Marinate steaks at room temperature for 20 minutes.

Heat a nonstick skillet over medium heat.

Remove steaks from marinade and discard any remaining marinade. Arrange steaks in the hot skillet; gently shake the skillet to avoid sticking. Cook for 1 1/2 minutes. Flip and cook 1 minute more. The tuna steaks should be seared on the outside while retaining a tender, rare center.