Preheat the oven to 325F/170C.
Spray a large baking sheet with non-stick spray.
Trim broccoli and cauliflower, cutting into bite-sized flowerets and reserving the stems for another use if desired.
Peel the onion and cut into slivers.
Put the vegetables into a large plastic bowl and drizzle with the olive oil.
Then sprinkle over the minced garlic, curry powder, and salt, and toss vegetables until they’re all coated with oil and seasonings.
Spread out on baking sheet. (Mine was a bit crowded; use two baking sheets if needed.)
Roast vegetables for an hour, or slightly longer, turning them every 20-25 minutes.
I would start checking after about an hour and remove from the oven when they’ve reached your preferred level of doneness. We cooked them an hour and ten minutes, for broccoli and cauliflower that still had a tiny bit of bite left.
Serve Roasted Broccoli and Cauliflower hot, with piece of lime to squeeze on at the table if desired.