For the fish, break up the achiote paste with a whisk or fork and mix with the oil until very smooth. Using a brush, coat fish with a generous layer of achiote marinade and let marinate in the fridge for at least 30 minutes and up to 1 hour while you prepare the salsa and vinaigrette.

Heat Griddle on a grill or on the stovetop over medium-high. Reserve 1 scallion from the bunch for garnish. Add the rest of the scallions and both serranos to the griddle with a drizzle of oil and sear, turning occasionally, until softened and blackened in places, 2–5 minutes. Set aside to cool.

For the vinaigrette, combine garlic, ginger, citrus juice, soy sauce, and sesame oil in a mixing bowl. Mince charred scallion, season with salt, and stir to combine. Taste and adjust seasoning, adding more citrus or salt, if needed. Chill until ready to serve.

For the avocado purée, peel and roughly chop the avocado and add to a medium bowl. Squeeze in the juice of 2 limes and use a whisk, potato masher, or spoon to break up any chunks and smooth out the purée. Remove stems and finely chop the charred serrano chiles and add to the bowl. Season with salt to taste and stir to combine.

Place Griddle over medium-high heat and drizzle with a little oil. Season fish on both sides with salt and pepper and place on griddle, cooking on one side until a deep brown crust forms, 5–7 minutes. Flip the fish and cook on the other side until cooked through, 5–7 minutes more. Transfer fish to a Sheet Pan to let it rest, about 5 minutes.

For the garnish, use Chef Knife to slice the radishes into ¼”-thick coins, then into ¼”-wide matchsticks. Slice the remaining raw scallion on a sharp bias and place both vegetables in a bowl of ice water to keep crisp. Drain after 2–3 minutes.

To serve, add a dollop of avocado purée to the plate. Place fish on top and drizzle with scallion vinaigrette. Top with the radish and scallion garnish and serve with tortillas, if desired.