Prepare rice noodles according to package instructions, leaving them slightly al dente as they will continue to cook later. When cooked, rinse them in cold water and toss in a little bit of oil to prevent them from sticking. Set aside.
Make the Sauce: In a small bowl, whisk together the soy sauce, chili paste, peanut butter, rice vinegar, fish sauce, brown sugar, 5 spice, and lime juice until smooth. Set aside.
In a large skillet or wok, heat 2 tablespoons of oil on medium-high heat. Add the thinly sliced chicken to the pan, and sprinkle with 1 teaspoon of 5 spice. Saute the chicken for about 3 minutes, then add onion and scallions to the pan. Continue to cook until the chicken and onions turn slightly golden in color, then add in garlic and cook for about 1 minute. Remove everything from the pan and set aside.
Lower the heat to medium, then add whisked eggs and continuously scramble for about 30 seconds. Add cooked chicken, onions, and garlic back into the pan along with the rice noodles, bean sprouts, and sauce. Gently fold all of the ingredients together, until evenly coated and heated through.
Garnish with chopped peanuts, cilantro, lime, and more scallion and bean sprouts.