Thaw fish, if frozen, and blueberries. For sauce: In a small saucepan, cook and stir onion and garlic in hot oil about 3 minutes or until softened. Add blueberries, vinegar, brown sugar, ginger, and lemon peel. Bring to boiling; reduce heat. Simmer, uncovered, about 15 minutes or until sauce has thickened and reduced to 1 cup.