Bring a large pot of salted water to a boil for the pasta. While waiting, dice the onion into 1/4-inch pieces, mince the garlic cloves, and slice the bell peppers into bite-sized chunks. Slice the kielbasa into 1/2-inch thick rounds. Having everything prepped and ready will let you move quickly through the cooking process without scrambling.

Add pasta to the boiling water and cook according to package directions until al dente. Meanwhile, heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Add the sliced kielbasa and brown it for about 5 minutes, stirring occasionally, until the edges are caramelized and the sausage releases its flavorful oils. This creates a flavorful base for the sauce.

Reduce heat to medium and add the diced onion to the kielbasa, cooking for about 5 minutes until softened and fragrant. Add the minced garlic and red pepper flakes, stirring constantly for about 1 minute to bloom the spices and release their flavors—this prevents the garlic from burning while allowing it to fully infuse the oil.

Pour in the canned diced tomatoes along with the Italian seasoning and stir well to combine. Let this simmer for 4-5 minutes, allowing the tomato flavors to meld with the kielbasa and aromatics. I like to add the seasoning early so it has time to fully dissolve and distribute evenly throughout the sauce.

Pour in the chicken broth and add the sliced bell peppers, stirring to combine. Simmer for about 5 minutes until the peppers begin to soften but still maintain some texture. The broth adds depth and balances the acidity of the tomatoes while the peppers add sweetness and body to the dish.

Drain the cooked pasta and add it to the skillet, tossing gently to coat everything evenly. Tear in the fresh basil and add the balsamic vinegar, stirring just until combined. The balsamic adds a subtle sweetness and acidity that brightens the entire dish. Taste and adjust seasoning if needed, then serve immediately topped with freshly grated Parmesan cheese.