Slice the sausage into 1/4-inch rounds. Prep all vegetables so they’re ready to go.
This cooks fast once you start.
Heat a large skillet over medium-high heat. Add 1 tablespoon of olive oil and the sausage. Cook 3–4 minutes, stirring once or twice, until browned on both sides.
Transfer sausage to a plate and keep the fat in the pan.
Sauté the firm veggies first. Add the remaining 1 tablespoon oil. Toss in broccoli and red onion with a pinch of salt. Cook 3–4 minutes, stirring occasionally, until they begin to soften and get some color.
Add the quick-cooking veggies. Stir in bell pepper, zucchini, and yellow squash.
Season with smoked paprika, Italian seasoning, red pepper flakes, and a little more salt and pepper. Cook 4–5 minutes, until crisp-tender.
Add garlic and sausage back. Make a small well in the center, add the minced garlic, and cook 30 seconds until fragrant. Return sausage to the skillet and toss everything together.
Finish with richness. Stir in the butter (if using) and adjust seasoning.
If you like brightness, squeeze in a little lemon at the end.
Serve hot. Sprinkle with chopped parsley and plate it up. It’s great on its own or with a simple green salad.