Preheat oven to 350 degrees F (175 degrees C). Line an oven-safe baking pan with aluminum foil or wax paper.
Place croutons into a food processor; blend until coarsely ground, about 30 seconds. Transfer to a plate.
Mix egg, salt, and pepper together in a bowl; dip eggplant slices into the egg mixture until coated. Transfer to crouton crumbs plate; coat eggplant in croutons. Placed breaded eggplant into prepared pan.
Bake in the preheated oven until breading is golden brown on both sides, 10 to 15 minutes per side.
Mix pasta sauce and garlic powder together in a bowl. Pour half of the sauce mixture into an oven-safe baking pan; top with half the Parmesan cheese.
Place baked eggplant onto Parmesan cheese layer; cover with mozzarella cheese. Pour remaining pasta sauce over mozzarella layer; top with remaining Parmesan cheese.
Bake in the preheated oven until Parmesan cheese is a light golden brown, about 25 minutes.