Prep the oven and pan: Preheat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.

Sweat the zucchini: Slice zucchini into half-moons about 1/4-inch thick. Toss with 1/2 teaspoon salt and spread on a sheet pan. Let sit 10–15 minutes to draw out moisture, then pat dry with paper towels.

Sauté aromatics: In a large skillet, warm olive oil or butter over medium heat. Add onion and cook 3–4 minutes until softened. Stir in garlic and cook 30 seconds until fragrant.

Soften the zucchini: Add zucchini to the skillet. Cook 4–6 minutes, stirring occasionally, until just tender and some moisture cooks off. Season with pepper and half the Italian seasoning. Remove from heat.

Make the creamy base: In a large bowl, whisk cream cheese until smooth. Mix in Greek yogurt (or sour cream) and chicken broth until creamy. Stir in remaining Italian seasoning, red pepper flakes if using, and half the Parmesan. Taste and adjust salt and pepper.

Combine the filling: Add cooked chicken, sautéed zucchini-onion mixture, and 1 cup shredded cheese to the bowl. Fold gently until everything is coated.

Assemble: Spread the mixture into the prepared baking dish. Top with the remaining shredded cheese and the rest of the Parmesan. If using, sprinkle breadcrumbs over the top for crunch.

Bake: Bake 18–22 minutes, until the edges bubble and the cheese is melted. For a golden top, broil on high for 1–2 minutes, watching closely.

Rest and garnish: Let the bake rest 5–10 minutes to set. Sprinkle with chopped parsley or basil before serving.