Using a fork, mix chile, garlic, cashew butter, lime juice, and 3 Tbsp. water in a small bowl to combine; season with salt. Set aside.
Place a rack in lowest position; preheat oven to 450°. Stir garlic, oil, cumin, and paprika in a small bowl to combine. Arrange cauliflower on a rimmed baking sheet and pour spiced oil over. Season with salt and toss to evenly coat cauliflower. Roast, undisturbed, until dark brown and crisp on the bottom, 15–20 minutes. Remove from oven and turn florets over. Continue to roast until second side is dark brown and crisp, 15–20 minutes longer.
Heat a large skillet over medium-high. Working in batches, toast tortillas in a single layer, turning halfway through, until warmed through, about 1 minute total. Transfer to plates.
Spread each tortilla with some reserved sauce; top with cauliflower. Garnish with onion, avocado, radishes, and cilantro. Serve with lime wedges for squeezing over.