Combine the Base Ingredients: Start by placing the chicken breast into your crockpot, breaking it up if necessary for even cooking. Pour in the two cans of coconut milk and the three cups of chicken broth, and then add two tablespoons of red curry paste. Use a wooden spoon to stir everything together until well combined, ensuring the curry paste is fully integrated.

Mix in the Flavors: Add the tablespoon of fish sauce, three tablespoons of lime juice, and two tablespoons of brown sugar. Fold these ingredients into the soup mixture, tasting as you go to adjust the seasoning if desired.

Add the Vegetables: Toss in the chopped onion and sliced red bell peppers. Stir once again to incorporate these fresh elements into the broth.

Set the Cooking Conditions: Cover your crockpot with the lid securely and set it to cook on low heat for 6–8 hours or on high for 3–4 hours.

Add the Final Touches: About 30 minutes before serving, incorporate the sliced mushrooms into the soup, stirring them carefully into the bubbling broth.

Shred the Chicken: Just before it's time to serve, use two forks to shred the chicken right in the pot, allowing it to meld into the soup.