Cook tortellini according to package directions. Meanwhile, in a large skillet, saute the mushrooms, garlic powder, onion powder and pepper in 1/4 cup butter until mushrooms are tender. Remove and keep warm.
In same skillet, combine milk and remaining butter. Bring to a gentle boil; stir in brick cheese. Cook and stir until smooth. Drain tortellini: place in a large bowl. Stir in the mushroom mixture and spinach. Add cheese sauce and toss to coat.
Transfer to a 3 qt. baking dish; sprinkle with mozzarella cheese. Cover and bake at 350 degrees for 15 minutes. Uncover; bake 5-10 minutes longer or until heated through and cheese is melted.