Bring a large pot of water to a boil. Meanwhile, toss the catfish, 1 tablespoon fish sauce, 1 teaspoon ginger, the turmeric and 1 teaspoon vegetable oil in a large bowl; set aside to marinate 15 minutes. Combine 3 tablespoons water with the remaining 1 tablespoon plus 1 teaspoon fish sauce and 1 teaspoon ginger, the lime juice, sugar and chili-garlic sauce in a small bowl; set aside.
When the water comes to a boil, turn off the heat, add the vermicelli and stir. Let sit until just tender, 2 to 3 minutes, then drain and rinse under cold water. Shake off as much water as possible and transfer to a large bowl. Add 1 teaspoon vegetable oil and half of the prepared sauce and toss; divide among 4 bowls.
Heat the remaining 1 tablespoon vegetable oil in a large nonstick skillet over medium-high heat. Add the fish and cook until browned, 2 to 3 minutes per side; remove to a plate. Add the bell pepper and scallions to the skillet and stir-fry until crisp-tender, 1 to 2 minutes. Stir in half of the herbs.
Top the noodles with the fish, vegetables and remaining herbs. Drizzle some of the remaining sauce on top and serve with more chili-garlic sauce on the side.