Prep the oven and pan. Heat oven to 375°F (190°C). Grease a 9x13-inch baking dish or similar casserole dish.

Season the chicken. Pat chicken dry and season both sides with 1 teaspoon salt and 1/2 teaspoon pepper. If the pieces are thick, slice breasts in half horizontally or cut into bite-size chunks for faster, more even cooking.

Par-cook the chicken. In a large skillet over medium-high heat, warm 1 tablespoon olive oil. Sear chicken 2–3 minutes per side (or 4–5 minutes total if in chunks) until lightly golden but not fully cooked. Transfer to a plate; it will finish in the oven.

Sauté aromatics and wilt spinach. In the same skillet, add a bit more oil if needed. Sauté onion 2–3 minutes until softened. Stir in garlic for 30 seconds. Add fresh spinach and cook until just wilted (or skip wilting if using frozen; just squeeze it dry very well).

Make the creamy base. In a large bowl, whisk together cream cheese, Greek yogurt, and mayonnaise until smooth. Stir in lemon zest, lemon juice, red pepper flakes, 1 cup mozzarella, and 1/2 cup parmesan. Season with 1/2 teaspoon salt and a few grinds of pepper.

Fold in veggies and chicken. Add the sautéed spinach mixture and the chopped artichokes to the bowl. Fold in the par-cooked chicken. Mix gently to coat everything evenly.

Assemble the casserole. Spread the mixture into the prepared baking dish. Top with remaining 1/2 cup mozzarella and 1/4 cup parmesan.

Add a crunchy topping (optional). Toss panko with 1 tablespoon olive oil or melted butter and a pinch of salt. Sprinkle evenly over the top for extra texture.

Bake. Place the dish on the center rack and bake 22–28 minutes, until bubbly around the edges and the top is lightly golden. The chicken should reach 165°F (74°C) in the center.

Rest and serve. Let the casserole rest for 5–10 minutes to set. Serve warm with a squeeze of fresh lemon and a crack of black pepper.