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.
Step 7. Bake for approximately 25 to 45 minutes at 350 degrees Fahrenheit. Cooking time depends on the oven temperature, quantity and size of steaks. For example, a 7-ounce tuna steak bakes in 20 minutes at 400 degrees Fahrenheit.