In a large bowl combine flour, sugar, baking powder, cinnamon, and salt. In a medium bowl beat egg yolks lightly with a fork. Beat in milk and oil. Add egg yolk mixture all at once to flour mixture. Stir just until moistened (batter should be slightly lumpy). Stir in chopped apple.
In a small bowl beat egg whites with an electric mixer on high speed until stiff peaks form (tips stand straight). Gently fold beaten egg whites into batter, leaving a few fluffs of egg white. Do not overmix.
Add batter to a preheated, lightly greased regular or Belgian waffle baker according to manufacturer's directions. Close lid quickly; do not open until done. Bake according to manufacturer's directions. When done, use a fork to lift waffle off grid. Repeat with remaining batter.
Serve warm with butter and warm maple syrup. If desired, top with fresh fruit.