Start by cooking the rice noodles according to the package instructions. If using fettuccine, cook until al dente. Once cooked, drain and rinse under cold water to stop the cooking process. Set aside.
In a large wok or skillet, heat the vegetable or peanut oil over medium-high heat. Add the sliced chicken breast and cook until it turns golden brown and is cooked through, about 5-7 minutes. Remove the chicken from the pan and set aside.
In the same pan, add the minced shallots, garlic, and red bell pepper. Sauté for about 2-3 minutes until softened. Then, toss in the matchstick carrots and cook for another 2 minutes.
Push the vegetables to one side of the pan and pour the beaten eggs into the empty side. Cook until scrambled and just set, then mix everything together in the pan.
Add the cooked chicken back to the pan along with the prepared noodles. Stir in the bean sprouts, green onions, and chopped cilantro.
In a small bowl, whisk together the brown sugar, soy sauce, fish sauce, lime juice, rice vinegar, peanut butter, and chili paste. Pour this sauce over the noodle mixture and toss everything together until evenly coated and heated through.
Dish out the Pad Thai onto plates and sprinkle with roughly chopped peanuts and additional cilantro if desired. A squeeze of lime juice adds a refreshing finish!