In a crockpot, combine chicken broth, lemongrass, ginger/galangal, lime zest, and red curry paste.
Cover and cook on high for 2-3 hours or low for 4-6 hours.
Using a slotted spoon, remove the onion, garlic, finger, lemon grass leaves leaving just the broth.
Add the chicken, coconut milk, and mushrooms. Season with salt and pepper.
Cover and cook on high for 1 hour or low for 2 hours until the chicken is cooked through and flavors are well combined.
Before serving, add lime juice, fish sauce (if using), and sweetener to crockpot.
Taste, adjusting seasoning if needed.
Serve hot with lime wedges, cilantro, and sliced red chilies for garnish.