Sauteé the chopped celery in butter for 5 minutes, stirring frequently. Remove from pan, set aside.
Brown the hamburger and drain off the fat. In a bowl stir in the croutons, Parmesan cheese and the beaten egg.
Spread this mixture over the bottom of a buttered 9 inch pie pan.
Mix the ground beef, garlic, onion, oregano, catsup, salt and pepper. (Please Note! You can use your favorite spaghetti sauce instead of catsup if you prefer). Place this mixture on top of the crust in the pie pan.
Bake in oven for 30 minutes at 350°F
Remove from the oven and turn up the temperature to 400°F
Cover the pie with the sliced mozzarella cheese slices and bake for 5 minutes until cheese is bubbling or melted.