Preheat the pan. Set a large skillet over medium-high heat and add 1 tablespoon of olive oil. Give it a minute to get hot; you want a lively sizzle when the sausage hits the pan.
Sear the sausage. Add the sliced sausage in a single layer. Cook 3–4 minutes per side until browned and slightly crisp at the edges.
Remove to a plate, leaving the flavorful fat in the pan.
Soften the onions and peppers. Add the remaining tablespoon of oil if the pan looks dry. Add onion and bell peppers with a pinch of salt. Cook 4–5 minutes, stirring occasionally, until softened and lightly caramelized.
Add zucchini and spices. Stir in zucchini, smoked paprika, oregano, and red pepper flakes.
Cook 3–4 minutes until the zucchini is tender but still has some bite. Season with salt and pepper.
Garlic and tomatoes. Lower the heat to medium. Add the garlic and cook 30 seconds until fragrant.
Stir in the tomatoes and cook 1–2 minutes until they just begin to release juices.
Return the sausage. Add the browned sausage back to the skillet and toss everything together. Warm through for 1–2 minutes so the flavors meld.
Finish with acid. Turn off the heat and splash in the balsamic vinegar or lemon juice. This brightens the whole dish.
Taste and adjust seasoning.
Garnish and serve. Scatter chopped parsley or basil on top. Serve as-is, or spoon over rice, polenta, or crusty bread. If using beans or spinach, fold them in at the end until warmed and wilted.