Preheat the oven to 425 °F . Lightly spray a foil-lined baking sheet with nonstick spray.
In a large bowl, mix together the broccoli, cauliflower, olive oil, salt, pepper and garlic powder
Spread the broccoli and cauliflower in an even layer on the prepared baking sheet.
Bake for 15 minutes, then give it a stir, put it back in the oven for another 5 minutes or so, until the vegetables are tender.