Bring 2 quarts of water to a rolling boil. Cook noodles for 2 minutes, then rinse extremely well under cold running water. (This will ensure the noodles are clean and free of the pungent dried rice flour odor.) Drain noodles in colander and spread out to dry for at least 20 minutes. The noodles will stick together, but don't be alarmed.
Meanwhile, heat the 2 tablespoons oil in a wok or large nonstick saucepan over moderate heat. Add garlic, shallots and chile paste and allow to sizzle until golden, about 30 seconds. Add catsup, sugar, fish sauce and salt and reduce slightly, about 1 minute. Add 2/3 cup chicken stock and reduce heat. Stirring frequently, simmer for 3 to 5 minutes. Remove 2 tablespoons of the sauce and set aside.
Add noodles to wok and using chopsticks, gently separate the noodles. Turn often and sauté until noodles absorb all the sauce and are cooked until just tender, about 5 minutes. Add bean sprouts, scallions and peanuts and fold into the noodles. Remove from heat and set aside.
Prawn Broccoli Stirfry:
Heat the 1 tablespoon oil in another nonstick pan over moderate heat. Add yellow onion and garlic and sauté until soft and aromatic, about 1 minute. Add the prawns. Toss in pan until they turn opaque, about 2 minutes. Add broccoli, reserved sauce and the 1/3 cup chicken stock. Cover and cook until vegetables are thoroughly hot, another 2 minutes.
To serve, portion noodles onto individual dinner plate and top with the prawns and broccoli stir-fry. Garnish with peanuts, cilantro and lemon wedges.