Brown the sausage: Heat 1 tablespoon olive oil in a large skillet over medium to medium-high heat. Add the sausage links and cook, turning occasionally, until well browned on all sides, about 8–10 minutes. Transfer to a plate; they will finish cooking later.

Soften the onions: Add the remaining 1 tablespoon olive oil to the same skillet. Add the sliced onion with a pinch of salt. Cook, stirring occasionally, until golden at the edges and softened, about 5–7 minutes. Scrape up any browned bits.

Add the peppers: Stir in the bell pepper strips and another small pinch of salt. Cook until tender-crisp and lightly charred in spots, 6–8 minutes. Keep the heat around medium-high so they blister a bit without steaming.

Stir in the aromatics: Add the minced garlic, oregano, basil, and red pepper flakes. Cook until fragrant, about 30 seconds. Don’t let the garlic brown.

Deglaze and build the sauce: Add the tomato paste and cook it for 1 minute to caramelize slightly. Pour in the diced tomatoes and, if using, the white wine or broth. Stir to combine and bring to a lively simmer.

Finish the sausage: Slice the browned sausage into 1/2-inch rounds and return them to the skillet. Nestle them into the peppers and sauce. Simmer, uncovered, until the sausage is cooked through and the sauce thickens a bit, 6–8 minutes.

Balance the flavors: Stir in the balsamic vinegar. Taste and season with salt and pepper. Add more red pepper flakes if you want extra heat.

Serve: Sprinkle with chopped parsley and spoon into warm rolls, over pasta, polenta, or rice. Add grated Parmesan if you like.