In a large saucepan, sauté the onion, celery, and garlic powder in canola oil until tender.
Stir in the stewed tomatoes, water, tomato paste, parsley, oregano, 1/2 teaspoon salt, 1/4 teaspoon pepper, and a bay leaf, then bring to a boil.
Reduce the heat, cover, and simmer for 1 hour. Remove the bay leaf and set the sauce aside.
In a skillet, cook ground beef over medium heat until no longer pink, breaking it into crumbles. Drain excess fat and set aside.
Combine flour, 3/4 teaspoon salt, and 1/4 teaspoon pepper in a shallow dish. Pour buttermilk into a separate shallow dish.
Dip each eggplant slice in buttermilk, then dredge it in the flour mixture.
Heat oil in a large skillet and fry the eggplant slices in batches until golden brown on both sides. Drain on paper towels.
Preheat your oven to 350°F. Grease a 13x9-inch baking dish and layer in this order: half the fried eggplant, Parmesan cheese, cooked beef, and tomato sauce. Sprinkle 1 cup of mozzarella cheese over the first layer.
Repeat with the remaining eggplant, Parmesan, beef, and sauce. Bake uncovered for 30 minutes.
Top with the remaining mozzarella cheese and bake for an additional 5–10 minutes, just until the cheese melts. Let the dish rest for 10 minutes before serving, then sprinkle parsley on top.