If possible, bring the cauliflower to room temperature before roasting to encourage better browning. Preheat the oven to 450°F (230°C) and position a rack in the center.
Remove the core and break the cauliflower into medium-large florets. Place them in a large bowl.
Whisk together the olive oil, kosher salt, cumin, chili powder, garlic powder, paprika, coriander, and black pepper until combined. Pour the spice mixture over the florets and toss by hand or with a spoon so each piece is evenly coated.
Arrange the coated florets in a single layer on a half sheet pan, leaving space between pieces so they roast instead of steam. Turn any flat sides down to maximize caramelization.
Roast until the cauliflower is deeply browned and tender, about 25 to 30 minutes, flipping once about halfway through to promote even color.
Transfer the roasted florets to a serving platter, squeeze the juice of ½ lime over them, scatter the chopped cilantro on top, and finish with a light dusting of flaky sea salt if desired. Serve right away.