Peel and slice onions into ½-inch rounds. Separate the rings. If your onions have very thin layers, keep two rings together. You don’t want your onion rings to be limp.
In a shallow bowl, combine cornstarch, flour, paprika, garlic powder, salt, and pepper. Stir in water to form a thick paste (resist the temptation to add more water). It will look like a glue. Place the panko crumbs into a second shallow bowl.
Add an onion ring to the batter and use a spoon to help coat the outside ring. Dip onion ring in the panko crumbs and use a spoon to help coat completely.
At this point, prepare your potato latkes mixture as per your favorite recipe.
Heat an inch of oil in a saucepan. When oil is hot, add onion rings and spoon the latke mixture in the middle of the onion and fry for 2-3 minutes, until latke is set. Flip over to other side. Drain on a cooling rack or paper towel. Serve with sweet chili sauce or your favorite dipping sauce.