Prep the produce and chicken: Cut the chicken into 1-inch pieces. Slice the zucchini, onion, and bell pepper.
Mince the garlic. Pat the chicken dry and season with 1/2 teaspoon salt, black pepper, and half the Italian seasoning.
Heat the skillet: Warm 1 tablespoon olive oil in a large skillet over medium-high heat. When the oil shimmers, add the chicken in a single layer.
Cook, undisturbed, for 2–3 minutes to sear, then stir and cook another 3–4 minutes until just cooked through. Transfer to a plate.
Sauté the veggies: Lower heat slightly to medium. Add the remaining 1 tablespoon olive oil.
Add onion and bell pepper with a pinch of salt and cook 3 minutes until softened. Stir in zucchini and cook 3–5 minutes until tender-crisp.
Add flavor boosters: Stir in garlic, remaining Italian seasoning, smoked paprika, and red pepper flakes. Cook 30–60 seconds until fragrant.
If using tomato paste, add it now and cook another minute to caramelize lightly. If using cherry tomatoes, stir them in to soften.
Bring it together: Return chicken and any juices to the skillet. Add a splash of broth to loosen browned bits and create a light sauce.
Simmer 1–2 minutes, stirring, until everything is hot and coated.
Finish and taste: Remove from heat. Stir in lemon zest and juice, and half the herbs. Taste and adjust with more salt, pepper, or lemon as needed.
Serve: Top with remaining herbs and a sprinkle of Parmesan or feta if you like.
Serve as-is, over rice or cauliflower rice, or with warm crusty bread.