Prep the aromatics: Mince garlic, grate ginger, slice scallions, and smash the lemongrass. Pat shrimp dry and season with a pinch of salt.
Sauté the base: Warm oil in a medium pot over medium heat.
Add the white parts of the scallions, garlic, and ginger. Cook 1–2 minutes until fragrant, not browned.
Add curry paste: Stir in red curry paste and cook 30–60 seconds to bloom the spices.
Build the broth: Pour in broth, add lemongrass, mushrooms, and bell pepper. Bring to a gentle simmer and cook 5–7 minutes until veggies start to soften.
Stir in coconut milk: Add coconut milk and fish sauce.
Keep heat at a gentle simmer. Taste and adjust salt if needed.
Cook the shrimp: Add shrimp and simmer 2–3 minutes, just until pink and opaque. Do not overcook.
Finish with greens and lime: Stir in spinach or bok choy to wilt.
Remove lemongrass. Add lime juice to taste and a pinch of coconut sugar if desired.
Garnish and serve: Ladle into bowls. Top with cilantro, Thai basil, green parts of the scallions, and sliced chili if you like it spicy.
Serve with lime wedges.