Whisk eggs, milk, and herbes de Provence together in a bowl until smooth. Dip 1 slice bread in the egg mixture until evenly soaked.
Melt butter in a skillet over medium heat; cook the dipped bread until slightly browned, 1 to 2 minutes per side. Transfer bread to a paper towel-lined plate. Repeat dipping bread in egg mixture and cooking in the skillet with remaining slices.
Cook and stir spinach in the same skillet over medium heat until wilted, 2 to 3 minutes. Layer spinach on top of 2 slices of French toast; top with apple slices and Cheddar cheese. Place a piece of French toast over Cheddar cheese layer creating a sandwich.