In a large pot, heat the vegetable oil over medium heat. Add the diced onion and sauté for about 3 minutes, until softened.
Stir in the minced garlic and grated ginger, cooking for an additional 1 minute until fragrant.
Add the sliced red bell pepper and mushrooms to the pot, cooking for another 3-4 minutes until they begin to soften.
Mix in the red curry paste and cook for 1 minute, stirring to combine with the vegetables.
Pour in the chicken broth and coconut milk, stirring well. Bring the mixture to a simmer.
Add the chicken pieces to the pot, cooking for about 10-12 minutes until the chicken is cooked through.
Stir in the fish sauce, brown sugar, and lime juice. Taste and adjust seasoning if necessary.
Serve hot over cooked rice or rice noodles, garnished with fresh cilantro and sliced green onions.
