Cook rice noodles according to package directions. Keep immersed in cold water until ready to use.
Make sauce and set aside. In a large wok or frying pan, add the oil, garlic, pork or chicken, or tofu and stir-fry for about 4 minutes. Add shrimp if using and cook until the shrimp are pink. Add sauce to the wok and toss gently. Add drained noodles, bean sprouts and peanuts to wok and toss gently.
Serve garnished with cilantro and scallions.