Cook and drain the spinach. Make sure you get most of the water out by pressing it against the side of a colander.
Cook the ground beef and drain.
Sauté the onion and mushrooms.
Make the cream of mushroom soup. After it has thickened, add 1/4 cup water and whisk to combine.
Combine the beef, onion, mushrooms, and spinach. I use the skillet I cooked the beef in (after draining it). The spinach will be somewhat stuck together after squeezing the water out. Break it up with your spoon or spatula and get it mixed in with the other ingredients.
Add the soup and cheese. Reserve about 1/2 cup of the cheese if you are not using tater tots.
Spread the mixture into a greased 9 x 13 inch baking dish.
Top with tater tots or the additional cheese.
If using cheese on top, bake at 350° for 20 – 30 minutes until hot and the cheese is melted. If using tater tots, bake at 375° 30 – 40 minutes until the tater tots are hot in the middle.
Recipe by The Gluten-Free Homemaker at http://glutenfreehomemaker.com/gluten-free-spinach-casserole/