Cook noodles according to package directions, drain.
While noodles cook, heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add steak; sauté 5 minutes, browning on all sides. Remove from pan; cover.
Melt butter in pan over medium-high heat. Add shallots and mushrooms; sauté 4 minutes. Add garlic; sauté 30 seconds. Stir in soy sauce. Sprinkle flour over mushroom mixture; cook 1 minute, stirring constantly. Gradually add broth, stirring constantly. Add pepper, salt, and thyme sprigs. Bring to a boil; cook 2 minutes or until thickened. Return beef to pan; cook 1 minute or until thoroughly heated. Discard thyme sprigs. Garnish with thyme leaves, if desired