Preheat oven to 425°F. Lower an oven rack to the bottom third of your oven, closer to the heat source. Place a large sheet pan in the oven to preheat along with the oven.
Slice your bell peppers and onion in ¼ inch thick strips, separating the onion pieces. Smash your garlic cloves with the flat side of your knife or the bottom of a bowl.
Finely chop your fresh rosemary and thyme. Gather your dried herbs, salt, and pepper.
Place all your peppers, onions, and smashed garlic in a large bowl. Add the herbs, salt, pepper, and olive oil and toss to evenly coat everything.
Remove the sheet pan from the oven and give a quick spritz with nonstick spray. Toss all the vegetables on the hot pan. Nestle the sausages in with the vegetables, trying to get each sausage to make contact with the hot metal. Bake at 425ºF for 20 minutes.
Remove the pan from the oven and use tongs to toss all the vegetables and turn the sausages over. There will be some moisture, which will evaporate while it finishes roasting. If there is an excess, just blot away with some paper towels. Place the pan back into the oven for 20 more minutes.
Remove the pan from the oven. Slice some or all of the sausages in half, if desired. Set the oven to broil and move the rack to 6 inches from the broiler. Place the pan under the broiler for about 5 minutes, or until the sausages get a nice brown color and the edges of the vegetables start to char just a touch. Watch carefully, as it can burn quickly.
Serve as is or make sausage and pepper sandwiches. Alternatively, dice up the sausages and serve everything tossed with pasta.