Prep the chicken and zucchini: Pat the chicken dry with paper towels.
Toss with salt, pepper, Italian seasoning, and smoked paprika. Slice zucchini into even half-moons so it cooks uniformly.
Heat the skillet: Set a large skillet over medium-high heat. Add 1 tablespoon oil and 1 tablespoon butter.
When the butter foams, tilt the pan to coat.
Sear the chicken in batches: Add half the chicken in a single layer. Don’t crowd the pan. Cook 3–4 minutes per side until golden and just cooked through.
Transfer to a plate and repeat with remaining chicken, adding another 1 tablespoon oil if needed.
Sauté the zucchini: Reduce heat to medium. Add 1 tablespoon butter to the skillet. Stir in the zucchini with a pinch of salt.
Cook 4–5 minutes, stirring occasionally, until lightly browned but still crisp-tender.
Add the garlic: Push zucchini to the sides. Melt the remaining 1 tablespoon butter in the center. Add minced garlic and red pepper flakes.
Stir 30 seconds until fragrant, not browned.
Deglaze and simmer: Pour in chicken broth (or wine) and lemon juice. Scrape up any browned bits. Let it bubble for 1–2 minutes to reduce slightly.
Bring it together: Return chicken and any juices to the pan.
Toss everything to coat in the garlic-butter sauce. Cook another minute to warm through. Taste and adjust salt, pepper, and lemon.
Finish and serve: Sprinkle with chopped parsley and Parmesan if using.
Serve hot with rice, orzo, crusty bread, or a simple green salad.