Preheat the oven to 450ºF. Slice onions into ½-3/4 inch rings, separate them and set aside.
Get a medium-size bowl and a shallow bowl ready. Using the medium-size bowl, make the batter by whisking the dairy-free milk and flour together until smooth. In the shallow dish, mix together the breadcrumbs and seasonings.
Set up your dredging assembly line from right to left starting with your sliced onions, then the batter, then the seasoned breadcrumbs and then a lined baking sheet.
Dip each ring into the batter, lightly shaking off any excess before dredging it in the seasoned breadcrumbs. Arrange them in a single layer on the prepared baking sheet and spray the tops of the onion rings with oil. Bake for 16 minutes, or until golden brown (they'll have varying shades of brown).