1 Add time each week to work your way up to 30 to 45 minutes of continuous exercise. 2  As you get stronger, try interval training once a week to help boost endurance and burn more calories.  Work your way up to 5 to 6 days of cardio and try to vary what you do and how hard you work.
To achieve a sear on the outside and keep it rare inside, place the tuna on the skillet or grill and let it sear for two minutes on the first side. Flip the tuna and let it cook for another two minutes, then remove it from the heat. Watch the tuna as it cooks to make sure you don't overcook it.
Grill the tuna steaks. Tuna steaks will usually need to cook for roughly 4 to 6 minutes per 1/2-inch (1.27-cm) thickness. Turn once in the middle of the cooking process to promote even cooking.1  Leave the grill uncovered if using charcoal but cover it if using gas.ransfer to a large resealable plastic bag. 1  The marinating step is only optional. 2  You can skip the marinade altogether and simply brush the tuna steaks with olive oil, lemon juice, and fresh herbs before cooking it. 3  Marinades penetrate into the tuna further, however, creating a more flavorful dish.