In a bowl, combine beef broth, cornstarch, soy sauce, garlic, and red pepper. Whisk until cornstarch dissolves. Set aside.
Season beef with salt and thinly slice. Add to the bowl and toss to coat. Cover and let marinate in the refrigerator for 10 to 15 minutes.
Bring a skillet sprayed with nonstick spray to medium-high heat. Add broccoli, sugar snap peas, mushrooms, scallions, and 1/4 cup of the marinade from the beef. Stirring occasionally, cook until broccoli softens, about 3 minutes.
Add beef and remaining marinade. Stirring occasionally, cook until beef is cooked through, 2 to 3 minutes.
Serve it up and season to taste with additional salt and garnish with sliced scallions, if using. Enjoy!