Cook the tortellini in boiling, salted water following package directions, drain. Preheat your oven to 400ºF. In a saucepan, prepare the white sauce mix following package instructions. Season with salt, pepper, and nutmeg. Gradually add 3/4 cup of grated cheese, cook, stirring constantly, until the cheese melts. Combine the tortellini, peas, mushrooms, and meatloaf in a buttered 1 quart casserole dish. Pour cheese sauce on top, toss gently to coat all ingredients with sauce. Sprinkle with remaining cheese and bake for 25 minutes or until golden brown and bubbly. Remove from oven and serve. Serves 4