Preheat the oven to 350°F (175°C).
Unroll one package of croissant dough and press it into the bottom of a 9×13-inch baking dish.
Bake the bottom crust for 7–9 minutes, or until lightly golden. Remove from oven and set aside.
In a large skillet over medium heat, cook the ground meat and diced onions until the meat is browned and the onions are soft. Drain excess grease.
Add chopped cabbage to the skillet. Sauté for 4–5 minutes until slightly wilted and tender. Season with salt and pepper to taste.
Spread the meat and cabbage mixture evenly over the baked croissant crust.
Sprinkle the shredded mozzarella cheese over the meat layer.
Unroll the second package of croissant dough and carefully place it over the cheese layer to form the top crust.
Bake the uncovered casserole at 350°F for 30 minutes.
Cover with foil and bake for an additional 10 minutes to ensure the top is soft and fully cooked.
Let it rest for a few minutes before slicing into squares. Serve hot.