Combine banana and lemon juice in a small bowl. Stir well; set aside.
Cut bread slices in half crosswise; cut a slit through cut sides of each piece of bread to form a pocket. Stuff 2 tablespoons banana mixture into pocket of each piece of bread.
Combine milk and next 6 ingredients (milk through eggs) in a large shallow dish, and stir well with a whisk. Arrange stuffed bread pieces in a single layer in dish, turning to coat. Cover and chill 45 minutes or until milk mixture is absorbed, turning bread pieces over after 20 minutes.
Melt 1 teaspoon margarine in a large nonstick skillet over medium heat; add half of bread pieces. Cook 4 minutes. Carefully turn bread over; cook 3 minutes or until browned. Repeat procedure with remaining margarine and bread pieces. Serve with maple syrup.