Grease pie plate, 10x1-1/2". Heat oven to 400~. Cook and stir onions and margarine in 10" skillet over low heat until onions are light brown. Sprinkle tuna, 1 c of the cheese and the onions in plate. Beat eggs, milk, baking mix, salt and peppeer 15 in blender on high or 1 minute with hand blender. Pour into plate. Bake 25 minutes. Top with remaining cheese to within 1" from edge. Bake 5 to 8 minutes longer or until knife inserted in center comes out clean (pie can be done even though some melted cheese adheres to knife). (wrv)