In your slow cooker, combine the chopped white onion, minced garlic, sliced red jalapeño, galangal, lemongrass, and lime leaves. Add the red Thai curry paste and chicken broth, stirring until well mixed.

Cover the slow cooker and set it to cook on HIGH for 3 hours or LOW for 6 hours.

After the cooking time is up, use a slotted spoon to remove the solid ingredients, leaving behind the fragrant broth.

Stir in the full-fat coconut milk, bite-sized pieces of chicken breast, and sliced white mushrooms into the flavorful broth.

Once the chicken is cooked through, add brown sugar, fish sauce, and fresh lime juice.

Ladle the creamy soup into bowls and garnish each serving with freshly chopped green onions and cilantro.