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) until tender. 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, then the minced garlic, curry powder, red curry paste, turmeric, and ground coriander. Sauté about 1 minute, stirring, until fragrant.
Add the remaining 1/2 tablespoon oil and the sliced red bell pepper; sauté another 1 minute.
Pour in the chicken broth and bring the mixture to a boil.
Stir in the coconut milk, then cover, reduce heat to low, and simmer 10 minutes.
Add 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.
Stir in the spinach, chopped cilantro, and lime juice; cook just until the spinach wilts.
Toss the cooked rice noodles into the soup to combine. Adjust seasoning as needed and serve warm topped with chopped peanuts and the chopped red chili (or drizzle with sriracha).