Preheat oven to 200°F.
Melt 2 teaspoons butter in a nonstick skillet over medium-high heat. Add strawberries and cook, stirring occasionally until slightly softened, about 3 minutes. Add maple syrup and continue to cook 30 seconds.
Remove from heat and stir in orange zest. Re-warm just before serving.
Whisk together eggs, egg white, milk and vanilla in a shallow dish or large bowl. Melt 2 teaspoons remaining butter in a large nonstick skillet over medium-high heat. Dip bread slices, one at a time into egg mixture, turning gently to coat both sides. Transfer slices to skillet a few at a time without crowding; cook 2 minutes on each side or until lightly browned. Keep warm on a baking sheet in the oven. Repeat with remaining 2 teaspoons butter and bread slices.
Serve French toast with warm strawberry mixture. Sprinkle with confectioners' sugar, if desired.