Preheat an outdoor grill for medium-high heat and lightly oil the grate.
Combine bell peppers and onions in a large bowl. Add olive oil, Italian seasoning, salt, and pepper; stir well to coat. Poke 4 holes in each sausage using a toothpick; this will help to prevent them from exploding on the grill.
Place vegetables in a grill basket and cook on preheated grill for 2 minutes. Add sausage directly to the grate and grill for 4 minutes. Flip sausage over, stir vegetables, and grill for 4 minutes more.