Place a 12" x 17" rimmed roasting pan into the oven and preheat the oven to 450°F.
Add the cauliflower florets to a large bowl. Drizzle with half the olive oil and fold to evenly coat. Drizzle with the remaining olive oil and fold to evenly coat.
In a small bowl, combine ground cumin, ground ancho chili, sea salt, and black pepper. Stir in the zest from the lime. Sprinkle half the spice mixture over the cauliflower, and fold to combine. Then sprinkle remaining spice mixture over the cauliflower, and fold again to combine.
Remove the hot pan from the oven and add seasoned cauliflower, spreading it out evenly across the pan. Place the pan back into the oven and roast for 15 minutes without stirring, letting the edges of the cauliflower caramelize.
In a small bowl or cup, combine melted butter and the garlic slices. Remove the hot pan of cauliflower from the oven and add the buttery garlic slices and the pepitas to the cauliflower. Toss to evenly combine, then place the pan back into the oven to roast for an additional 5 minutes, or until the cauliflower is nicely caramelized.
Remove the pan from the oven. Sprinkle with a bit more sea salt and black pepper, if desired. Serve straight from the pan, or transfer the cauliflower to a serving platter. Cut the zested lime in half and squeeze the juice over the top of the cauliflower. Sprinkle with chopped cilantro to finish. Serve hot, with additional fresh lime wedges to squeeze over individual portions.
