In a large, heavy-bottom pot over medium heat, heat up the olive oil, add in the chicken, season with salt and pepper. Cook the chicken until brown and nearly cooked through.
Add in the onion and red bell pepper and cook until softened and the onions are somewhat translucent.
Add in the garlic and cook until fragrant.
Add in the Thai red curry paste and garlic - stir to combine all the contents entirely. Allow the curry paste to become fragrant and toast slightly.
Add in the broth, coconut milk, and lemon grass. Stir to combine and let it come to a bubbling, high simmer.
Once simmering, add in the brown sugar and fish sauce. Stir to combine, reduce the heat to a low simmer, let cook for 20 minutes, allowing the flavours to combine.
In the meantime, bring another pot filled with water to a boil and cook the noodles according to the package instructions, making them al dente (they will cook further in the hot soup and you don't want them to become mushy).
Once the soup has simmered for 20 mins, remove the lemon grass and begin preparing your soup bowls.
First, place a some noodles in the bottom of the bowl, top with the soup, add a handful of bean sprouts and top with a sprinkle of the cilantro, basil and green onions. Squeeze a wedge of lime juice overtop and garnish with an additional wedge.
Serve hot and if you want added heat, add in some sriracha!