Bring a large pot of salted water to a boil and add the penne pasta, cooking according to package directions until al dente. While the pasta cooks, chop the onion into bite-sized pieces, cut the bell peppers into 1-inch strips, mince the garlic cloves, dice the tomatoes, and slice the kielbasa into 1/2-inch thick rounds. Tear the fresh basil leaves by hand into smaller pieces—this preserves more of their delicate flavor compared to cutting. Drain the pasta when ready and set aside.

Heat the olive oil in a large skillet over medium-high heat. Add the kielbasa slices and brown them for about 5 minutes, stirring occasionally until the edges are caramelized and the fat renders—this creates a flavorful base for the sauce. Add the chopped onion and cook for another 5 minutes, stirring frequently until softened and slightly translucent. I like to let the onions pick up some color from the bottom of the pan; this adds depth to the final dish.

Add the minced garlic and crushed red pepper to the skillet and cook for 1 minute, stirring constantly until fragrant—this brief cooking blooms the spices and releases their essential oils without burning the garlic. Pour in the diced tomatoes and Italian seasoning, then cook for 4-5 minutes, stirring occasionally. The tomatoes should begin to break down slightly and concentrate their flavors.

Pour the chicken broth into the skillet and add the bell pepper strips, stirring to combine all ingredients. Bring the mixture to a gentle simmer and cook for 5 minutes until the peppers are tender-crisp—they should retain some texture rather than becoming mushy. I prefer my peppers to have a slight bite, so I don't overcook them at this stage.

Add the cooked pasta from Step 1 directly to the skillet and toss everything together until well combined. Remove from heat and stir in the balsamic vinegar and torn basil leaves—the acidity from the vinegar brightens the dish and the fresh basil adds a final layer of flavor. Divide among serving bowls and top each portion with grated parmesan cheese.