Pat fish fillets dry with a paper towel and lightly season both sides with salt. Set aside.

In a large shallow pan, heat olive oil over medium heat. Add sliced onions, minced garlic, and ginger. Sauté for 1–2 minutes until fragrant and softened. Add red chilis (or chili flakes) and scallions and cook for another 30 seconds to release its aroma.

Pour in the coconut milk and broth. Add fish sauce, sugar, lime zest, lime juice, and a pinch of salt to taste. Stir to combine and bring to a gentle simmer.

Carefully add the fish into the simmering coconut lime broth. Reduce heat to low and poach, covered, for 7–9 minutes, or until the fish is opaque and flakes easily with a fork. Taste broth again and add any additional salt as needed to taste.

Carefully transfer the fish to serving plates. Spoon the coconut broth over the top and garnish with chopped scallions and a drizzle of chili oil. Serve with steamed white rice and your favorite vegetables.