Prepare grill (medium-high heat). Brush sausages and onions with 3 tablespoons dressing; grill sausages until cooked, 15 minutes, and onions until charred, 10 minutes. Toss greens with remaining dressing; mound on plates. Slice 4 sausages (reserve 2 for pizza). Top greens with sausages, cheese, figs, and mint.