Jazz up grilled or broiled fish with a tasty sauce that combines fresh pineapple, ginger, and tamari. Tuna is terrific with this Asian-inspired glaze, but the glaze will also pair well with halibut, mahi-mahi, or other firm-fleshed fish. This glaze can be made several days in advance; reheat before using.
Place the pineapple and 2 tablespoons of pineapple juice in a blender or small food processor. Process until smooth. Transfer the purée to a saucepan and add the tamari, brown sugar, and ginger. Bring the mixture to a boil over medium heat, stirring to dissolve the sugar.
Meanwhile, combine the cornstarch with the remaining 2 tablespoons of pineapple juice and stir until smooth. Set aside.
Place a fine mesh sieve over a clean bowl and strain the pineapple and ginger sauce, discarding solids that won't push through the sieve. Return the strained sauce to the pan and place over medium heat. When the sauce reaches a boil, stir in the cornstarch slurry and cook, stirring once or twice, until the glaze boils. Cook for one minute, then remove the pan from the heat and let the glaze cool.
Prepare your grill for a medium-hot fire. Rub the fish on both sides with some of the oil, and then season with salt and pepper. Grill the tuna for 3 minutes on one side, then turn the fish over and cook another 2 to 3 minutes for medium-rare. Brush some of the pineapple glaze over the top of each piece of fish, cover the grill, and cook another 30 to 60 seconds. Serve immediately, with more hot pineapple glaze on the side.