Adjust rack to upper third of the oven and preheat to 400°F. Prepare a parchment-lined sheet pan.
In a medium bowl, stir together the tamarind chutney, sugar, two-thirds of the fish sauce, rice vinegar, sriracha, garlic, and ginger.
Place snapper fillets onto parchment-lined sheet pan. Sprinkle flesh sides of red snapper fillets with Kosher salt and freshly ground black pepper. Brush a thin layer of the tamarind glaze onto the flesh side of the fillets, covering it all. Reserve leftover glaze for later use.
Roast for 10 minutes. Remove from the oven and brush with another layer of glaze. Return to the oven and cook for an additional 2 minutes, until cooked through and flaky.
Meanwhile, make the slaw. In a medium bowl, combine the shredded cabbage, cashews, crispy onions, chili pepper, cilantro, lime juice, sesame oil, avocado oil, the remaining fish sauce, and a big pinch of Kosher salt. Toss to combine. Taste and season with more salt, if needed.
Serve fish alongside slaw and enjoy!