Add to Crockpot: Place chicken, bell pepper, mushrooms, onion, garlic, ginger, red curry paste, and chicken broth into the slow cooker.
Cook: Cover and cook on low for 6-7 hours or high for 3-4 hours, until the chicken is fully cooked and tender.
Shred & Stir: Remove the chicken, shred it, then return to the crockpot. Stir in coconut milk, fish sauce, brown sugar, lime juice, and season with salt and pepper. Let cook for another 10-15 minutes on high.
Garnish & Serve: Ladle soup into bowls and top with fresh herbs. Serve as-is or with jasmine rice or noodles.