Bake for a total of 20-30 minutes or to desired doneness. The broccolini seems to require just 15 minutes, while the cabbage, bell pepper, and cauliflower benefit from a longer roast – up to 25-30 minutes. (Once steamed), the starchy vegetables shouldn’t need more than 20 minutes in the oven. Steamed Brussels need to be roasted for 15 minutes, while unsteamed Brussels can roast for up to 20-25 minutes. Just watch the oven closely and check for doneness.