Place the rice noodles in a large bowl, pour in enough very hot tap water to cover and let them soak for 30 minutes. Drain the noodles and set aside.
Stir together the tamarind paste with boiling water in a bowl until well mixed; let the mixture stand for 15 minutes. Press the paste mixture through a fine-mesh sieve and discard any fibres or seeds. Combine the sieved tamarind paste with the ketchup, lime juice, soy sauce, sugar and chilli paste in a bowl.
Heat the vegetable oil in a wok over medium-high heat until the oil shimmers. Cook and stir the garlic and tofu until the tofu begins to show brown edges, 3 to 4 minutes. Pour in the eggs and scramble for 30 seconds, then add the noodles, tamarind mixture and bean sprouts. Cook and stir until the noodles are separated, heated through and covered with sauce, about 5 minutes. Sprinkle with peanuts and sliced spring onions.