01 -
Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Adjust the oven rack to the upper third position. Coat a 9x13-inch baking dish evenly with cooking spray.
02 -
In a large nonstick skillet, melt butter over medium heat. Add the chopped onion, sliced garlic, Italian seasoning, crushed red pepper, and ¾ teaspoon of the kosher salt. Cook, stirring frequently, until the onions are softened and translucent, approximately 4 minutes.
03 -
Stir in the flour and continue to cook, stirring constantly, for 1 minute. Gradually add the milk, continuing to stir constantly to prevent any lumps, until the mixture slightly thickens, about 3 minutes.
04 -
Incorporate the cream cheese and the remaining 1 teaspoon of salt into the sauce, stirring until the cheese is fully melted and the mixture is homogeneous. Remove the skillet from the heat. Stir in the shredded chicken, cooked rice, drained spinach, lemon juice, and lemon zest until all ingredients are evenly distributed.
05 -
Transfer the prepared mixture into the greased baking dish, spreading it out into an even layer. Evenly sprinkle the shredded mozzarella and grated Parmesan cheeses over the top. Place the dish in the preheated oven and bake until the cheese on top is melted, approximately 15 minutes.
06 -
After baking, turn the oven to broil. Broil the casserole for 2 to 3 minutes, or until the cheese is golden brown and bubbly.