• Preheat the oven to 400°F and adjust the oven rack to the center position.

For Sausage and Veggies:

• In a large skillet or Dutch oven over medium-high heat, add the Italian sausage pieces. Cook them while stirring occasionally until they develop a nice golden color, which should take about 5 minutes.
• Next, lower the heat to medium and add the sliced bell peppers, onion, and minced garlic. Cover the pan and let it cook for approximately 10 minutes, stirring from time to time, until the vegetables become tender.
• Add the diced tomatoes along with their juices and season with salt and pepper. Allow the mixture to come to a gentle boil, then let it simmer without a lid for another 10 minutes to meld the flavors.

For Pasta:

• Meanwhile, cook the pasta in a large pot of salted boiling water until it is just underdone, about 2 minutes shorter than what the package recommends. Make sure to drain it thoroughly.
• Incorporate the drained pasta into the sausage and vegetable mixture, setting aside half of the mozzarella and Parmesan cheeses. Stir everything together to ensure the pasta is well-coated and cheesy.
• Pour the prepared mixture into a large casserole dish or a 9x13 baking pan. Top it with the remaining mozzarella and Parmesan cheeses as an even layer.
• Bake the dish uncovered for around 25 minutes, or until the cheese becomes melted, bubbly, and has a golden appearance. Allow it to rest for about 5 to 10 minutes before serving. Enjoy your meal!