Cook ravioli according to the package directions. Drain and set aside.
In a large cast-iron or non-stick skillet, sauté chopped onion and 1 lb ground beef in 1 tablespoon olive oil until meat is no longer pink.
Stir in a jar of marinara sauce and simmer for 15 minutes. Mix in 2 cups of fresh spinach and season with salt and pepper to taste. Remove from the heat.
Spread a little of the meat sauce on the bottom of a 9x13" casserole dish and then cover with half the ravioli. Spoon half the meat sauce on top, then sprinkle with half (1 cup) of the cheese.
Repeat layering in the same order, ending with the last cup of cheese on top; bake for 15 minutes. Let stand 10 minutes before serving. Enjoy!
Notes
Cook ravioli al dente. They will continue to cook in the sauce while baking, and you don't want them to get mushy.
We used Rao's jarred marinara, but feel free to make your own!
To get the last bit of marinara sauce off of the sides of the jar, add ¼ cup water (or red wine) to it, close the lid and shake. Empty the jar into the meat sauce.
You can use Italian bulk sausage instead of ground beef. Also, don't be afraid to mix your ground meat for the sauce. Combine beef with pork, or use chicken and turkey.
Mix some parmesan cheese with mozzarella.
It's OK to replace spinach with kale or Swiss chard. You can even use cheese and spinach stuffed ravioli instead.
For the best results, read additional tips in the post above.
Please keep in mind that nutritional information is a rough estimate and can vary significantly based on products used.