As NoelH290 says, either with a small sprayer that is suitable for oil. This keeps the amount to a minimum and gives the food a certain chrunch. Or simply put the frozen fries in a bowl before baking, drizzle 2-3 teaspoons of oil over them and shake a few times to distribute the oil. I have achieved an acceptable solution with both. With fine-cut fries it is a little better.

It's just a cute little oven. You can drizzle oil over the food like I do.