Combine flaxseed and sliced almonds in a shallow dish. Combine milk and next 5 ingredients (through egg whites) in a medium bowl, stirring well with a whisk, and pour milk mixture into another shallow dish.
Working with 1 bread slice at a time, place bread slice into milk mixture, turning to coat both sides. Let bread stand in milk mixture 2 to 3 minutes. Remove bread slice from milk mixture; dredge 1 side of bread in flaxseed mixture, pressing gently to adhere. Repeat procedure with remaining bread slices, milk mixture, and flaxseed mixture.
Heat a large nonstick skillet over medium heat. Coat pan with cooking spray. Melt 1/2 teaspoon butter in pan; swirl to coat bottom of pan. Add 3 coated bread slices, coated sides down; cook 2 minutes on each side or until lightly browned. Repeat procedure with cooking spray, remaining butter, and remaining coated bread slices. Sprinkle powdered sugar evenly over toast.