Whisk together the chili paste, soy sauce, lime juice, peanut butter, veg-oyster sauce and sugar in a bowl. If using tofu, slice it into cubes or triangles and marinade in the sauce for at least half an hour.
Soak the rice noodles in a bowl of warm water for about half an hour, then drain thoroughly. Meanwhile, peel and thinly slice the shallots and garlic, and diagonally slice the spring onions into 1cm pieces.
Heat a wok over medium-high heat and add the oil. If using the tofu, lift it out of the sauce with a slotted spoon, stir fry until golden brown and set aside. Put the vegetables in the wok and stir-fry for two minutes. Then add the rice noodles and sauce. Stir-fry for a few minutes, mixing well, until the noodles are nearly cooked.
Add the bean sprouts and greens, and mix well. Once the noodles are cooked, stir in the coriander and peanuts, and serve at once with tofu pieces on top.