3 asparagus buns Recipes

vegetable oil, plus more for grill grate, asparagus, trimmed, sweet onion, cut into 1-inch rings, bell pepper, trimmed, cored, and quartered, portobello mushrooms, stems and gills removed, salt and freshly ground black pepper, prepared pesto sauce, cajun mustard, ciabatta buns, halved and toasted, crumbled goat cheese