Slice the onion into round pieces, ¾ to 1 inch thick.
Brush each round with oil and add seasoning.
Grill the rounds directly on the grill grate over medium heat for 5 to 7 minutes per side. If they are sticking to the grill, they are not ready to flip.
Remove and serve.
Notes
You can season the onion rounds with just salt and pepper, but try using different seasonings for enhanced flavor.