Preheat your oven to 350 degrees Fahrenheit, setting the stage for baking.
Prepare the base: Unroll one package of refrigerated croissants and lay them flat in the bottom of your 9x13 pan. Bake for 7-9 minutes until golden, then remove from the oven.
Cook the meat: In a skillet, brown the ground beef or turkey with the diced onions until fully cooked, then drain any excess fat.
Incorporate the cabbage: Add the chopped cabbage to the skillet, allowing it to cook slightly with the meat and onions, infusing the flavors.
Assemble the casserole: Layer the meat and cabbage mixture over the baked croissant base, then sprinkle evenly with shredded Mozzarella cheese.
Add the final layer: Top with the second package of croissants, carefully unrolling and placing them over the cheese.
Bake to perfection: Return the casserole to the oven, uncovered, for 30 minutes. Then, cover with foil and bake for an additional 10 minutes to soften the top layer.
Serve and enjoy: Once baked, let the casserole cool slightly, cut into squares, and serve warm, inviting everyone to savor this Midwestern delight.