When cooking tuna in a frying pan, it is best to use a bit of oil to prevent sticking and to create a crispy outer crust. Place the tuna in the hot pan and cook for about 3 minutes per side, or until it is browned and cooked through. You can also grill tuna by placing it on a preheated grill and cooking for 3-5 minutes per side, or until it is browned and cooked through.