In a large bowl, gently stir together chicken, 1 cup bread crumbs, 1 egg, salt, pepper, and onion powder until well combined. Divide mixture into 36 portions; shape each portion into a ball. Press 1 cheese cube into each ball; pinch and roll ball to seal.
In a medium bowl, place remaining 2 cups bread crumbs. In another bowl, whisk together remaining 3 eggs. Dredge meatballs in bread crumbs to coat. Dip meatballs in eggs, letting excess drip off. Dredge meatballs again in bread crumbs to fully coat.
In a 12-inch cast-iron skillet, add oil to a depth of ¼-inch, and heat over medium heat until hot. Working in batches, cook meatballs, turning occasionally, until golden brown, 3 to 5 minutes. Remove meatballs with a slotted spoon, and let drain on paper towels. Pour off oil from skillet.
Pour sauce into skillet; nestle meatballs in sauce. Top with sliced mozzarella; sprinkle with Parmesan.
Bake until cheese is melted and sauce is bubbly, 25 to 30 minutes. Let stand for 5 minutes. Sprinkle with oregano.
Recipe by Southern Cast Iron at https://southerncastiron.com/cheese-stuffed-chicken-meatball-parmesan/