Preheat your oven to 375°F (190°C). Cook the lasagna noodles according to package directions until al dente. Drain and set aside.

In a large saucepan, melt butter over medium heat. Whisk in the flour and cook for 1 minute. Gradually pour in the milk, whisking constantly. Add garlic powder, onion powder, nutmeg, salt, and pepper. Simmer, stirring often, until the sauce thickens (about 5-7 minutes). Remove from heat and stir in 1/4 cup of the Parmesan cheese.

In a medium bowl, mix together the ricotta cheese, egg, 1/4 cup Parmesan cheese, and chopped parsley until well combined.

Spread a thin layer of white sauce in the bottom of a 9x13-inch baking dish. Layer with noodles, half of the ricotta mixture, half of the shredded chicken, one-third of the mozzarella, and one-third of the white sauce.

Repeat the layers once more: noodles, the remaining ricotta mixture, remaining chicken, another third of the mozzarella, and another third of the white sauce.

Add a final layer of noodles. Top with the remaining white sauce, the rest of the mozzarella, and the remaining Parmesan cheese.

Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and continue to bake for an additional 15-20 minutes, or until the top is golden and bubbly.

Let the lasagna rest for at least 10 minutes before slicing. Garnish with fresh parsley and serve warm.