If using frozen cauliflower, break up any frozen clumps, but do NOT defrost.
Mound cauliflower rice, onion, celery, carrots and garlic in the center of a sheet pan coated with non-stick cooking spray.
Drizzle olive oil over the top and toss to combine. (I use my hands!)
Spread cauliflower rice and vegetables into an even layer on the sheet pan. Season with salt and pepper or wait and season to taste at serving time.
Roast mixture in the oven for about 20 minutes, turning the rice half-way through with a spatula or large spoon. If cooking from frozen, it will take about 25 minutes.
Remove cauliflower rice vegetable pilaf from oven to serving bowl, scraping up all the browned bits on the pan.
Toss with additional mix-ins if using (see notes) and enjoy!