Sauté aromatics (optional but recommended): In a small skillet, warm the coconut oil over medium heat. Add onion and cook 3–4 minutes until softened.
Stir in garlic, ginger, and curry paste; cook 1 minute until fragrant. Transfer to the crockpot.
Load the crockpot: Add bell pepper, carrots, mushrooms, and chicken (or tofu) to the slow cooker. Pour in broth, fish sauce, and brown sugar.
Stir to combine.
Cook low and slow: Cover and cook on Low for 5–6 hours or on High for 2.5–3 hours, until chicken is tender and vegetables are soft. If using shrimp, wait to add it until the last 20–30 minutes of cooking.
Finish with coconut milk: Stir in coconut milk and continue cooking on Low for 20–30 minutes. Don’t boil after adding the coconut milk to keep the broth silky.
Season to taste: Add lime juice and taste the broth.
Adjust with more lime for brightness, soy sauce for salt, or a pinch more brown sugar for balance.
Add greens and herbs: Stir in spinach or kale until just wilted, 2–3 minutes. Ladle into bowls and top with cilantro, basil, and chili if you like heat.
Serve: Enjoy as-is, or pour over cooked rice or rice noodles for a heartier meal. Serve with lime wedges.