Before I 'recipe,' I just have to mention - The 'Squattier' the Vidalia Onion, the Sweeter the Vidalia Onion.
I slice off the top, then try to slice off the hairy part of the root end, leaving the in-the-onion part of the root there. I peel the coloured (I'm Canadian, eh) skin from the onion and lay it, top down, on my board.
Slicing through the root 'portion,' I cut the onion into wedges; the remaining root portion will hold the onion together.
Spray or dip in EVO and sprinkle with a bit of Coarse Salt. Lay the pieces on your hot BBQ so the grills will caramelize (mark) the flat/cut sides.
As the onion cooks, the concentric parts of each wedge will 'Blosom, or bloom - spread and seperate.
Really great - the heat activates the sugars within the onion; the caramelization add flavours too.
Hope you enjoy them.