Prep the sausage. If using links, prick each link a few times with a fork. For quicker cooking, slice into 1-inch rounds.
Keep the sausage chilled until you’re ready to cook so it browns better.
Brown the sausage. Heat 1 tablespoon olive oil in a large skillet over medium-high. Add the sausage in a single layer. Cook until browned on both sides and cooked through (6–8 minutes for slices; 10–12 minutes for whole links).
Transfer to a plate and tent with foil.
Sauté the veggies. In the same skillet, add the remaining 1 tablespoon olive oil. Add peppers and onions with a good pinch of salt. Cook, stirring occasionally, until softened and lightly caramelized, about 8–10 minutes.
Add aromatics. Stir in the garlic, Italian seasoning, and red pepper flakes.
Cook until fragrant, about 30 seconds. Don’t let the garlic burn.
Build the sauce. Add the tomato paste, stirring to coat the vegetables. Pour in the chicken broth and scrape up the browned bits.
Simmer 2–3 minutes until slightly thickened.
Finish with acidity. Stir in the balsamic vinegar. Taste and adjust salt and pepper. The vinegar should brighten the flavors without overpowering them.
Bring it together. Return the sausage and any juices to the pan.
Toss to combine and warm through for 2–3 minutes. If the pan looks dry, add a splash more broth.
Garnish and serve. Sprinkle with chopped parsley. Serve on its own, over brown rice or cauliflower rice, tucked into a whole-wheat roll, or alongside a crisp salad.