In a dutch oven, heat coconut oil over medium heat.
Add the onion and garlic and saute for 2-3 minutes, stirring frequently, until the onion is soft.
Add the lemongrass paste and the red curry paste and stir to mix.
Add the chicken stock and galangal (or ginger), stir, and bring to a boil.
Reduce the heat to low and simmer for 20 minutes, uncovered.
Strain the liquid in a fine mesh sieve to remove the aromatics. I prefer to skip this step and just remove the galangal (or ginger root) and keep the onions and garlic in the stock for more texture.
Add the strained liquid back to the pot and bring it to a boil. This is where you would add the thinly sliced chicken breast to the pot if swapping for the shrimp. As soon as it reaches a boil, reduce the heat to low.
Add the coconut milk, mushrooms, cilantro stems, fish sauce, lime juice, and brown sugar.
Simmer this mixture for 10 more minutes.
Add in the shrimp and cook for 1 1/2 to 2 minutes until just pink.
Serve immediately garnished with a lime wedge, cilantro, green onions, and chili oil for drizzling.