Preheat oven to 375 degrees.
Set aside 1/4 C of each of the grated cheese. This will be used for the topping.
Prepare the pasta al dente, according to package instructions. Drain and add the cooked pasta to a shallow casserole dish. Add the shredded chicken and spinach to the casserole dish as well. Mix to combine.
Melt the butter in a saucepan over medium heat.
Add the flour and whisk to create a paste. Slowly add the chicken stock and milk, whisking until combined. Cook for about 8 minutes, whisking until the sauce begins to thicken.
Remove from heat and add the cheese not being used for the topping. Whisk until melted and thickened.
Add the artichoke pesto and lemon juice. Mix well.
Pour the cheese sauce over the pasta, chicken and spinach. Mix to combine.
Sprinkle the remaining cheese on top and season with cracked pepper.
Cover with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 10 - 15 minutes until the cheese is bubbling and slightly browned. Serve immediately.
I used the Artichoke Lemon Pesto, by Bella Cucina, in this recipe.