Preheat oven to 350.
Mix the oil and spices in the bowl, add the potatoes, and stir until coated.
Spread the potatoes in a single layer on the cookie sheet, and use the rubber spatula to scrape all the oil out of the bowl as you drizzle it over the potatoes. Sprinkle with onions and rosemary.
Bake for 30-40 minutes, until the potatoes are golden brown and slightly crunchy.