3/4 pound rigatoni or some other short pasta
1/2 medium head cauliflower (about 1 pound), cut into florets
8 ounces Brussels sprouts, trimmed and halved (quartered if large)
1 medium red onion, cut into 1/2-inch wedges
2 sprigs fresh thyme
4 tablespoons olive oil
kosher salt and black pepper
2 ounces grated pecorino (about 1/2 cup), plus more for serving