Preheat a convection oven to 425°F (220°C) and line a heavy-gauge baking sheet with parchment paper.
In a large mixing bowl, combine cauliflower florets with olive oil, cumin, smoked paprika, chili powder, garlic powder, and salt; toss until surfaces are uniformly coated.
Spread the cauliflower in a single layer on the baking sheet and roast for 20 minutes, rotating the pan halfway through, until edges exhibit dark caramelization.
In a small bowl, whisk together the Greek yogurt, cilantro, and lime juice until the consistency is smooth; adjust salt to taste.
Heat a cast-iron skillet over medium-high heat and toast each corn tortilla for 30 seconds per side until pliable and slightly charred.
Construct each taco by placing 1/8 of the roasted cauliflower into a warm tortilla, topping with shredded cabbage and radish slices, and drizzling with 1 tablespoon of cilantro yogurt crema.
Serve immediately with lime wedges on the side.