To roast the garlic for the glaze, cut about 1/2 inch off the top of the garlic head. Cut the roots so that the garlic will sit flat. Remove most of the papery skin, but leave enough so that the cloves stay together. Place the head in a small casserole dish or baking pan, drizzle the olive oil over it, and cover it with a lid or foil. Bake for 1 hour. Remove the garlic and let it cool until you can handle it.
Combine the water, pineapple juice, teriyaki sauce, soy sauce, and brown sugar in a medium saucepan over medium/high heat. Stir occasionally until the mixture boils, then reduce heat to simmer.
Squeeze the sides of the head of garlic until the pasty roasted garlic is squeezed out. Measure 2 tsp into the saucepan and whisk to combine. Add the remaining glaze ingredients and stir.
Simmer for 40-50 min or until the glaze has reduced by about 1/3 and is thick and syrupy. Make sure it doesn't boil over. When the glaze is done, cover the saucepan and set it aside until the fish is ready.
To cook the fish, preheat grill to med/high heat. Remove any skin or bones from the fillets. Brush the entire surface with a light coating of the butter spray. Lightly salt and pepper both sides and place them on the grill at a slight angle so that grill marks will be made. Cook for 2-4 minutes and turn them over. After 2-4 minutes, turn them over at a different angle so that the grill marks will criss-cross. Cook 2-4 minutes more, flip again and cook until done.
The entire cooking time should be between 8-15 min depending on the thickness of the fillets and the heat of the grill.
When the fillets are done, remove from grill and spoon a generous portion of glaze over each one. Serve hot.