Preheat the oven: Set to 400°F (200°C).
Line a baking sheet or 9x13-inch baking dish with parchment for easy cleanup.
Prep the zucchini: Trim the ends. Slice each zucchini lengthwise. Use a spoon to scoop out the centers, leaving a 1/4-inch border to create boats.
Reserve about half of the scooped zucchini flesh and chop it finely.
Season and par-bake: Place the zucchini boats cut-side up. Brush with 1 tbsp olive oil and season with salt and pepper. Bake for 10 minutes to soften slightly, then remove and set aside.
Sauté aromatics: While the boats bake, heat the remaining 1 tbsp olive oil in a skillet over medium heat.
Add onion and cook 3–4 minutes until softened. Stir in garlic and cook 30 seconds until fragrant.
Add zucchini and deglaze: Stir in the chopped zucchini flesh and a pinch of salt. Cook 2–3 minutes to reduce moisture.
Pour in chicken broth and simmer 1 minute to pick up any browned bits. Remove from heat.
Make the filling: In a large bowl, combine cooked chicken, cream cheese, mayonnaise, Italian seasoning, smoked paprika, red pepper flakes (if using), 1/2 cup mozzarella, and Parmesan. Add the warm onion-garlic-zucchini mixture.
Mix until creamy. Taste and season with salt and pepper.
Stuff the boats: Spoon the filling evenly into each par-baked zucchini shell. Press gently to pack it in.
Top with the remaining 1/2 cup mozzarella.
Bake to melt: Return to the oven and bake 15–18 minutes, until the cheese is melted and the filling is heated through.
Broil for color (optional): Switch to broil for 1–2 minutes to get golden, bubbly tops. Watch closely to prevent burning.
Finish and serve: Let rest 5 minutes to set. Garnish with chopped parsley or basil.
Serve warm.