Preheat oven to 400ºF. Prepare a rimmed sheet pan (appr. 13 x 18 inches) by spraying it with olive oil spray or cooking spray. Place Italian sausages on sheet pan.
In a medium bowl, stir together bell pepper, onion, olive oil, salt, and pepper until vegetables are coated with olive oil and seasonings. Arrange around the sausages in an even single layer on the prepared sheet pan.
Place the pan in the preheated oven and bake for 15 minutes. Stir vegetables and flip sausages. Return to oven and continue cooking for another 15 minutes or until vegetables are tender and sausage is cooked to at least 165ºF when checked with an instant read thermometer.
Notes
You can bake more sausages or fewer. I based this recipe on a 19 oz. package with 5 sausages. Nutrition information is calculated for 1.5 lb. sausage (5 servings) and includes the vegetables.
Sausages (no vegetables): Omit the vegetables, olive oil, salt and pepper and keep the baking time the same. Use a smaller sheet pan.
With added vegetables: If desired, make this a sheet pan dinner. Add more vegetables, such as cubed or baby potatoes, cubed sweet potatoes, sliced carrots, or mushrooms (as many as will fit on the pan in a single layer or divide between 2 pans).
Frozen sausages: Increase cooking time slightly, about 10 minutes. You don’t need to thaw them first.
Smoked/precooked sausages: Add them to the pan after 15 minutes, when you stir the vegetables.