Preheat oven to 375F/190C. Spray a large glass or ceramic casserole dish with non-stick spray or brush with a little olive oil.

Mix the Better Than Bouillon Beef Base with ¼ cup water; then simmer the mixture on the stove until it's reduced to 1 tablespoon thick stock. Let it cool.

Heat a couple of teaspoons olive oil in a large heavy frying pan and cook the beef over medium-high heat until it's completely browned. Put browned beef in the casserole dish.

Wash mushrooms and spin dry in a salad spinner, or let them drain well.

Chop up the cauliflower and pulse in the food processor to make cauliflower rice.

Cut drained mushrooms into quarters. Heat a couple more teaspoons olive oil in the frying pan and cook mushrooms until they have lost all their liquid and are slightly browned. Put mushrooms in the casserole dish.

Mix the sour cream and mayo and add the cooled and reduced stock and stir together.

Chop an onion into small pieces. Heat two more teaspoons oil in the frying pan, add the onions, and cook until softened and starting to brown.

Add the cauliflower rice, 1 tsp. steak seasoning, salt, and pepper to the frying pan with the onions. Cook about 3 minutes, or until cauliflower is partly cooked.

Add the onion-cauliflower rice mixture to the casserole dish and gently combine all the ingredients.

Mix the 1 cup grated Mozzarella, Parmesan, and ½ tsp. steak seasoning into the mayo-sour cream mixture.

Gently mix the sauce into the cauliflower rice-ground beef mixture in the casserole dish.

Top the casserole with 1 cup (or more) grated Mozzarella.

Bake casserole 30-40 minutes, or until it's bubbling hot and the top is lightly browned.

Serve hot.