Heat waffle iron. Whisk together flour, baking powder, sugar and salt in a large mixing bowl. Stir milk, egg and butter into flour mixture until just combined. Fold in ham and cheese.
Mist waffle iron with nonstick cooking spray. Pour about 3/4 cup batter onto iron and spread to edges with a spatula. Cook until waffles are golden, 8 to 10 minutes. Repeat with remaining batter, misting iron with cooking spray as needed. Serve immediately.