Bring a large pot of salted water to a boil. Add pasta and cook 1–2 minutes shy of package directions for al dente finish (reserve 1 cup pasta water before draining).

While the pasta cooks, heat 1 tbsp olive oil in a large skillet over medium-high heat. Add sliced sausages and brown on both sides, 3–4 minutes.

Remove sausages from the skillet and set aside. Lower heat to medium; add remaining olive oil, onions, and zucchini. Sauté for 4–5 minutes until zucchini is tender-crisp and onions are translucent.

Add garlic and tomatoes; cook until tomatoes begin to blister, about 2–3 minutes. Sprinkle in oregano and red pepper flakes if using.

Deglaze skillet with chicken broth or white wine, scraping up brown bits. Stir in tomato paste if using, then return sausages to the pan.

Drain pasta and add directly into the skillet. Toss everything gently for 1–2 minutes so pasta absorbs flavors.

Finish with grated Parmesan and chopped parsley. If sauce is too thick, add a splash more pasta water; if too thin, simmer briefly to reduce.

Plate and serve warm with additional herbs or a squeeze of lemon.