Slice beef into ¼ inch slices across the grain. Place in a zip top bag. Add to bag the soy sauce, vinegar and chili flakes. Using hands, distribute sauce evenly throughout beef slices. Let sit on counter top for one hours, or up to 4 hours in refrigerator.
Break broccoli florets into small chunks. Make noodles from the broccoli stems by using a spiralizer or cut into ¼ inch slices and then into ¼ inch noodles.
Remove beef slices from marinade. Heat a large skillet or wok to medium high heat. Add oils. Cook the beef until lightly browned and remove from skillet. Add in garlic and cook for one minute. Add in broccoli stem noodles and broccoli florets and saute until softened. Add in reserved marinade and add beef slices back in. Cook until sauce is thickened slightly. Serve immediately.
Recipe by Healthy Family Recipes at http://www.apronstringsblog.com/broccoli-beef-with-broccoli-stem-noodles/