Preheat and prep: Heat oven to 375°F (190°C). Grease a 9x13-inch baking dish. Pat chicken dry and season with salt, pepper, and paprika.

Sauté the chicken: Warm olive oil or butter in a large skillet over medium-high heat. Add chicken and cook 4–6 minutes, just until no longer pink on the outside. It will finish cooking in the oven. Transfer to a plate.

Soften aromatics: In the same skillet, add the onion (if using) and cook 2–3 minutes until soft. Add garlic and cook 30 seconds until fragrant. Turn off heat.

Wilt the spinach: Add fresh spinach to the warm skillet and stir until just wilted. If using frozen spinach, make sure it’s fully thawed and squeezed dry before adding.

Make the creamy base: In a large bowl, whisk together cream cheese, sour cream, mayonnaise, and heavy cream until smooth. Stir in lemon zest (if using), red pepper flakes, and half of the mozzarella and Parmesan.

Add the veggies: Fold the artichoke hearts and the spinach mixture into the creamy base. Taste and adjust seasoning with salt and pepper.

Combine with chicken: Add the sautéed chicken and any juices to the bowl. Mix until everything is evenly coated.

Assemble: Spread the mixture into the prepared baking dish. Top with the remaining mozzarella and Parmesan for a golden, cheesy crust.

Bake: Bake uncovered for 20–25 minutes until bubbly and the top is lightly browned. Chicken should reach an internal temperature of 165°F (74°C).

Rest and serve: Let the casserole rest for 5–10 minutes so it sets. Garnish with chopped parsley. Serve warm.