How to Make It
Bring a large pot of water to a boil. Add salt. In a small bowl, stir the tomato paste with the garlic, ginger, paprika, turmeric and water.
In a large skillet, heat the peanut oil. Add the onion and cook over moderately high heat, stirring occasionally, until it begins to brown, about 5 minutes. Add the tomato paste mixture and cook, stirring constantly, until fragrant, about 2 minutes. Add the shrimp and cook until they are just opaque, about 3 minutes. Add the fish sauce, rice vinegar, sesame oil and half of the scallions. Remove from the heat.
Boil the noodles for about 1 minute; drain and reserve 1 cup of the noodle cooking liquid. Add the noodles to the skillet and toss to coat. Stir in the reserved noodle liquid and cook, tossing, for 1 minute longer. Season with salt. Transfer the noodles to plates, garnish with the remaining scallions and serve with lime wedges.