When I worked in a "smashed hamburger" restaurant, we had a lot of fried and breaded vegetables on the menu. Besides french fries and onion rings, we had fried mushrooms, zucchini and jalapeno peppers. I would put a basket of fried vegetables into the fryer for maybe two or three minutes, then hang it on a rack to drain.
If a customer ordered three hamburgers and an order of fried zucchini, I'd portion out some par-cooked zucchini sticks and deep fry them until they were crispy and brown. If I had to cook them completely from raw, it would have taken at least 8 minutes to reach that point. The hamburgers would be done in 5 minutes at most. We par-cooked a lot of foods so they would all come out at the same time when ordered.