Bring 4 cups of water to a boil in a large saucepan. Add the pad thai rice noodles and cook according to package directions (about 3–6 minutes). Drain and rinse under cold water; set aside.
Heat 1 tablespoon of the oil in a large pot over medium-high heat. Add the chopped onion and sauté about 3 minutes until softened.
Add 1/2 tablespoon oil, the minced garlic, curry powder, red curry paste, turmeric, and ground coriander. Sauté 1 minute until fragrant.
Add the remaining 1/2 tablespoon oil and the sliced red bell pepper; sauté about 1 minute.
Pour in the chicken broth and bring the mixture to a boil.
Stir in the coconut milk, cover, reduce heat to low, and simmer for 10 minutes.
Stir in the shredded chicken, snow peas, brown sugar, fish sauce, and chopped green onions. Season with salt to taste and cook 2 minutes to heat through.
Add the spinach, chopped cilantro, and lime juice; cook until the spinach wilts, about 1–2 minutes.
Toss the cooked noodles into the soup to combine. Serve warm topped with chopped peanuts and chopped red chili pepper or a drizzle of sriracha.