Preheat a grill to medium. Place the pizza dough on a baking sheet and brush with 1 tablespoon olive oil; set aside. Grill the sausages, turning often, until cooked through, about 8 minutes. Transfer to a cutting board and slice into 1/4-inch-thick rounds; set aside.
Combine the bell peppers, parsley, red onion, the remaining 2 tablespoons olive oil, and the balsamic vinegar in a medium bowl. Season with salt and pepper and toss to coat; set aside.
Stretch the pizza dough into a 12-inch round. Place the pizza dough directly on the grill grates; cook until the crust is golden and marked, about 5 minutes. Flip the crust and spread with the marinara sauce. Top with half of the cheese, then the sausage and the remaining cheese. Cover and grill until the cheese melts and the crust is cooked through, about 6 more minutes. Remove the pizza from the grill; let sit 5 minutes before slicing. Serve with the bell pepper salad.