In a bowl, gently coat the halibut with 1/2 tablespoon of fish sauce while you prepare the other ingredients.

In a mortar and pestle, pound together garlic, cilantro roots, white peppercorns, Thai chilies, and spur chilies until it resembles a rough paste (about 2-3 minutes).

In a wok, heat a couple of tablespoons of vegetable oil over medium heat. Add the herb paste and sauté until it starts to turn golden (about 2 minutes).

Increase the heat to high. Add the marinated fish and quickly toss it with the herb mixture, coating it well.

Pour in the remaining fish sauce, sugar, and a splash of water; toss to combine.

Add the fingerroots and young green peppercorns, mix, and cook the fish without stirring until it's done, flipping halfway (about 5-7 minutes). Add more water to prevent sticking if needed.

Once the fish is cooked through, turn off the heat and toss in the Thai basil leaves until just wilted.

Serve alongside jasmine rice or any grain of your choice.