Rough chop all of the root vegetables into about 1/4 inch slices.
Chop the onion into 8 sections.
Toss the chopped vegetables in a large bowl with the avocado oil, sea salt and rosemary (optional).
Spread out on a cookie sheet, and bake at 400 degrees for about 45 minutes, tossing and turning once or twice while they're cooking, until the vegetables are tender through.