Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta and set aside.

In a large skillet, heat the olive oil over medium heat. Add the Italian sausage, breaking it apart with a wooden spoon, and cook until browned and cooked through (about 5-7 minutes).

Add the sliced onion, red bell pepper, and yellow bell pepper to the skillet with the sausage. Sauté for about 5 minutes until the vegetables are softened.

Stir in the minced garlic and cook for an additional 1 minute until fragrant.

Add the drained diced tomatoes and Italian seasoning to the skillet. Cook for another 3-4 minutes, allowing the flavors to meld. Season with salt and pepper to taste.

Toss the cooked pasta into the skillet with the sausage and peppers. If the mixture seems dry, add reserved pasta water a little at a time until you reach the desired consistency.

Serve warm, garnished with fresh basil leaves and grated Parmesan cheese if desired.

Feel free to customize the dish by adding other vegetables such as zucchini or mushrooms.

For a lighter version, consider using turkey or chicken sausage.

Store leftovers in an airtight container in the refrigerator for up to 3 days. Reheat on the stovetop or microwave before serving.