Preheat the oven to 400 degrees F (204 degrees C).
Place the cauliflower in a large bowl. Drizzle with olive oil, and sprinkle with garlic powder (if using), salt, and pepper. Toss to coat.
Arrange the cauliflower in a single layer on a large baking sheet. (Do not crowd the pan – each floret should be touching the pan.) You can use a non-stick sheet pan like this, or line any type of sheet pan with foil and coat lightly in oil to prevent sticking.
Roast cauliflower in the oven for 25-30 minutes, tossing halfway through, until browned on the edges. (Cook time is for florets about 1 inch in diameter and 1.5-2 inches long; it will vary with larger or smaller florets.)