1. Turn all burners to medium-high and heating grill with lid down until very hot, about 15 minutes. Scrape grate clean with grill brush

2. Meanwhile, combine onions, fennel, fennel fronds, salt, and pepper in medium microwave-safe bowl. Cover with plastic wrap and microwave on high power until onions begin to soften and tips turn slightly translucent, 4 to 6 minutes, stirring once halfway through cooking (be careful of steam). Transfer onions and fennel to disposable roasting pan. Place sausages in single layer over onions and fennel and wrap roasting pan tightly with foil.

3. Place roasting pan in center of grill, cover grill, and cook 15 minutes. Move pan to one side of grill and carefully remove foil cover. Using tongs, place sausages directly on grate. Grill sausages, covered, turning every 1 to 2 minutes, until golden brown on all sides, 5 to 7 minutes. Transfer sausages to platter and loosely tent with foil. Cover grill and continue cooking onions and fennel, stirring occasionally, until liquid evaporates and onions begin to brown, 5 to 10 minutes longer. Serve sausages, passing onions and fennel separately.

Serves 4