Unbeatable Chicken Manicotti

Ingredients

• 1 (8-ounce) package manicotti
• 3 cups chicken, cooked and shredded
• 1 (10-ounce) package frozen spinach, defrosted and drained
• 2 1/2 cups ricotta cheese
• 1 1/2 cups mozzarella, shredded and divided
• 3/4 cup parmesan, freshly grated and divided
• 1 teaspoon Italian seasoning
• kosher salt, to taste
• ground black pepper, to taste
• red pepper flakes, to taste
• 4 tablespoons butter
• 2 cloves garlic, minced
• 1/4 cup all-purpose flour
• 2 1/2 cups milk
• 1/2 cup parmesan, freshly grated
• juice of 1/2 a lemon
• 2 tablespoons parsley, plus more for garnish, freshly chopped