Prep the zucchini bowls. Preheat your oven to 400°F (200°C). Halve the zucchini lengthwise and use a spoon to scoop out the centers, leaving about 1/4-inch walls.
Brush with olive oil and season with salt, pepper, and garlic powder. Place cut-side up on a parchment-lined baking sheet.
Pre-bake for tenderness. Bake zucchini for 10–12 minutes until just starting to soften. You want them tender but still holding their shape.
Cook the chicken. While the zucchini pre-bakes, heat oil in a large skillet over medium-high.
Season chicken with Italian seasoning, onion powder, garlic powder, salt, and pepper. Sear 5–7 minutes, stirring occasionally, until browned and cooked through. Transfer to a plate.
Make the Alfredo sauce. In the same skillet, reduce heat to medium.
Add butter and garlic; cook 30–60 seconds until fragrant. Pour in heavy cream and bring to a gentle simmer. Whisk in Parmesan (and cream cheese if using) until smooth.
Add a pinch of nutmeg, then season with salt and pepper. Simmer 2–3 minutes until slightly thickened.
Combine chicken and sauce. Return chicken to the skillet and toss to coat. The sauce should be velvety and cling to the meat.
Fill the bowls. Spoon the creamy chicken mixture into each zucchini half.
Top with mozzarella and a sprinkle of extra Parmesan.
Bake to finish. Return to the oven for 8–10 minutes, until the cheese melts and turns golden at the edges. If you like a deeper color, broil for 1–2 minutes, watching closely.
Garnish and serve. Let cool for a couple of minutes. Finish with parsley and crushed red pepper flakes if you want a little heat.
Serve warm.