Cut the beef into thin strips and slice the onion. Heat 2 tablespoons of oil in a large skillet over a high flame. Season the beef with salt and pepper. Saute the beef until it just begins to brown. Add the orange juice, bouillon cubes and pepper flakes. Simmer until the beef is just done. If the sauce is thin, strain through a colander, reserving the beef. Return the sauce to a saucepan over a high heat. Reduce until the sauce reaches a desirable consistency or thicken with a little cornstarch.