Heat an ovenproof skillet over medium-high heat; add the oil. Once hot, add ground beef, celery, onion, and garlic. Cook, breaking up meat, until no longer pink, 5-6 minutes.
Stir in marinara sauce, salt, and pepper. Reduce heat to low. Simmer, stirring occasionally.
In a large bowl, stir together ricotta, half of mozzarella, Parmesan, eggs, Italian seasoning, minced garlic, garlic powder, and pepper. Spread over meat mixture.
Sprinkle with remaining mozzarella cheese. Cover and cook on medium-low heat until cheese is hot and cooked through, 10-15 minutes. Broil until top is browned, 2-3 minutes. Let stand 10 minutes before serving.
Notes
Feel free to adjust seasonings and cheese types as preferred. Perfect for a low-carb dinner!