Cook the rice noodles according to the package instructions. Use salted boiling water. Stir gently so they do not stick. Drain them well and rinse with cold water. This stops overcooking. Set the noodles aside while you prepare the soup base.

Place a large pot over medium heat. Add vegetable oil. Once warm, add chopped onion. Stir slowly until soft and glossy. Add garlic and ginger next. Cook for one minute. The smell should feel warm and inviting.

Spoon the red curry paste into the pot. Stir it with the aromatics. Let it cook for two minutes. This step wakes up the flavors. The oil will turn red and fragrant. Keep stirring so nothing burns.

Slowly pour coconut milk into the pot. Stir gently to blend it with the curry paste. Add chicken broth next. Bring everything to a light simmer. The soup should look creamy and smooth. Lower the heat slightly.

Add sliced chicken to the simmering soup. Stir gently so pieces separate. Add bell pepper and mushrooms. Let everything cook for eight minutes. The chicken should be tender and cooked through. The vegetables should stay slightly crisp.

Add fish sauce and brown sugar. Stir well. Taste the broth carefully. Add more curry paste if needed. Adjust salt if required. Squeeze in fresh lime juice. This brightens the soup and balances the richness.

Add the cooked noodles into the pot. Stir gently so they soak up the broth. Let them heat for two minutes. Do not overcook. The noodles should stay soft but firm.

Ladle the soup into bowls. Top with fresh cilantro and green onions. Add chili oil if you like heat. Serve hot. Enjoy every spoon slowly.