Soak the rice noodles according to the package directions. Rinse them with cold water and drain well. Drizzle the noodles with a little oil to keep them from sticking, and toss to coat.
In a small bowl, stir together the tomato sauce, fish sauce, lime juice, brown sugar, chili sauce, and tamarind concentrate (if using).
Heat a good drizzle of oil in a large nonstick skillet set over medium-high heat. Add the meat or shrimp if they’re uncooked (if your meat is cooked, set it aside for now), along with the tofu and the chilies if you’re using them. Cook for a few minutes, until the meat is cooked through or the tofu is golden. Push the mixture aside or remove it from the pan. If you are using shrimp, remove them from the pan so that they don’t overcook and become tough. Add the eggs and cook them as if you were making scrambled eggs, breaking them up with a spatula. Push them aside.
Add a little more oil if you need it and stir fry the garlic and green onions for about a minute. Add the noodles and cook, tossing them with tongs, for another minute. Return any reserved cooked meat to the pan, pour as much of the sauce as you want over it all, and cook for 2-3 minutes, tossing the mixture with tongs or a spatula to coat everything with sauce and heat it through. Add the bean sprouts at the very end as you toss everything together.
Serve immediately in large shallow bowls. Sprinkle with chopped peanuts and serve with lime wedges to squeeze over top.