Prep the chicken and veggies. Pat the chicken dry and cut it into small, even pieces.
Slice the zucchini and onion, and mince the garlic. Have everything ready to go—the cooking moves fast.
Season the chicken. In a bowl, toss the chicken with 1 tablespoon olive oil, smoked paprika, oregano, black pepper, and 1/2 teaspoon salt. The oil helps the spices cling and the chicken brown well.
Brown the chicken. Heat a large skillet over medium-high heat.
Add the seasoned chicken in a single layer. Let it sear undisturbed for 2–3 minutes, then stir and cook until browned and just cooked through, about 5–6 minutes total. Transfer to a plate and keep warm.
Soften the aromatics. Lower heat to medium.
Add the remaining 1 tablespoon olive oil to the same pan. Add the onion with a pinch of salt and cook 2–3 minutes until translucent. Stir in the garlic and red pepper flakes; cook 30 seconds until fragrant.
Cook the zucchini. Add the zucchini and a small pinch of salt.
Spread into a single layer and let it sit for 1–2 minutes to get some color. Stir and cook 3–4 minutes more until just tender with a slight bite. Avoid overcooking.
Deglaze and combine. Pour in the chicken broth and scrape up any browned bits.
Return the chicken and any juices to the pan. Stir to coat.
Finish with lemon and Parmesan. Turn off the heat. Add lemon zest and juice.
Taste and adjust salt and pepper. If using, sprinkle in Parmesan and toss gently.
Garnish and serve. Top with chopped parsley or basil. Serve hot as is, or over rice, quinoa, or cauliflower rice.