Whisk yogurt and maple syrup to blend in small bowl. Set aside. Combine banana and orange concentrate in medium bowl. Using fork, mash to coarse paste. Spread banana mixture on two bread slices. Top each with a second bread slice, pressing to adhere. Beat whites and milk in shallow bowl to blend. Melt butter in large nonstick skillet over medium heat. Dip both sides of each sandwich briefly into milk mixture and add to skillet. Cook until brown, about 3 minutes per side. Transfer French toast to plates. Serve with maple yogurt.