Toss beef with salt and pepper. In a large skillet, heat oil over medium-high heat; saute beef 2 minutes. Add garlic and green onion; cook and stir until beef is browned, 2-3 minutes. Remove from pan., In same skillet, heat butter over medium-high heat; saute asparagus and mushrooms until asparagus is crisp-tender. Add beef, soy sauce and lemon juice; heat through, tossing to combine. Serve with rice.