MIX soy, garlic, oil and lemon juice. - MARINATE the tuna in the soy mixture for 15-30 minutes (do not over marinate). - PUT steaks on hot grill and cook 10 minutes per inch of thickness for well done. For rare, cut the cooking time in half. - REMOVE from grill. - SERVE atop grilled vegetables. - POUR half of the soy butter on each steak and serve.