Coat grill rack with nonstick cooking spray and preheat grill to medium-high heat.
Place sausages on one side of the grill, and peppers and onion on the other side of the grill. Grill 15 to 20 minutes, turning occasionally. Grill sausage until an instant-read thermometer registers 165°F. Grill peppers and onion until charred.
Transfer to a cutting board. Cut sausages, peppers and onion into slices.
To assemble salad, place arugula and radicchio in 4 salad bowls. Top with sausage, peppers and onion. Drizzle evenly with vinegar and oil. Season with freshly ground pepper to taste, and serve.