Bring a pot of water to a boil. Add gluten free pasta and cook for 8 to 10 minutes or until al dente. Drain.

Warm a nonstick skillet over medium heat and melt 1 tablespoon butter. Saute thinly sliced beef, 3 minutes per side. Remove beef from pan.

Add onions, mushrooms, and garlic to the pan. Saute until onions are translucent. When the onions soften, add sliced sirloin back to the pot. Pour the soup over the steak and vegetables, and cook until hot and bubbly.

Remove from heat and add light sour cream or Greek yogurt,  and salt & pepper to taste.

Serve mixture over noodles with steamed green beans or broccoli on the side.