In a large saute pan, heat 2 tablespoons of the olive oil over medium-high heat. Add the sausage to the skillet and brown on all sides, 10 to 12 minutes. Transfer the sausage to a plate.
Add the bell peppers, onions and remaining 1 tablespoon of olive oil to the saute pan used for the sausage and cook, stirring occasionally, until the vegetables are soft, about 10 minutes. Add the tomato paste and garlic. Let cook for 1 minute, and add the chicken stock. Cut the sausages on the diagonal into 2-inch pieces and add them to the saute pan. Cook until the sauce is slightly thickened, about 5 minutes. Season with salt and pepper.
Fill the toasted rolls with the sausages, peppers and onions and serve warm.