Preheat the oven to 425°F (218°C). Adjust the oven rack to the middle position and line a rimmed baking sheet with parchment paper.
Cut the cauliflower into quarters. Then cut away the thickest part of the core. Pull the florets apart with your fingers or cut them away from the rest of the head with the tip of a paring knife. You want the florets to be 1 1/2 inches or so in size. You should have about 4 generous cups florets.
Dump the cauliflower in a large bowl. In a small bowl, whisk together the oil, chili powder, paprika, salt, and a good grinding of black pepper. Pour the oil mixture over the cauliflower florets and toss to thoroughly coat.
Spread the cauliflower in a single layer on the parchment, making certain to leave some space between the florets, and roast, stirring once, for 20 to 30 minutes. You want the cauliflower to be deep golden and beginning to crisp at the edges.
Serve the roasted cauliflower with the lime wedges and cilantro sauce, if desired.