Preheat the oven to 350 degrees F. Lightly coat a 9X13-inch pan with nonstick cooking spray. Set aside.
In a large saucepan, melt the butter over medium heat. Add the onion and garlic and cook, stirring often, until the onion is translucent and tender, 3-4 minutes. Stir in the flour and let it cook, stirring constantly, for 1-2 minutes.
Gradually add the chicken broth and milk while whisking vigorously. Continue cooking and stirring for 4-5 minutes until the mixture simmers and thickens. Stir in the basil, oregano, salt and pepper.
To assemble, spread about 1 to 1 1/2 cups sauce on the bottom of the prepared pan. Place 3 no-boil noodles on top and dollop with 1/2 of the ricotta. No need to spread the ricotta out into an even layer, although you can press it down a bit, just spoon it across. Add half of the chicken on top of the ricotta.
Layer on 1/2 of the chopped spinach. It will seem like a lot but just spread it evenly - it will cook down while baking. Sprinkle 1/2 of the mozzarella and 1/2 of the Parmesan cheese (don't forget to take out 1/4 cup of the Parmesan for sprinkling across the top!).
Place 3 noodles over the top, gently pressing down to compress the layers below. Spread 1/2 of the remaining sauce over the top. Repeat the layers again (remaining ricotta, chicken, spinach, mozzarella, Parmesan).
Place the last 3 noodles over the top, pressing down again. Spread the remaining sauce over the top and sprinkle with reserved Parmesan cheese.
Cover the baking dish with lightly greased aluminum foil and bake for 30 minutes. Uncover and bake for 15 minutes until golden and bubbly. Let the lasagna rest for 10 minutes. Sprinkle with chopped parsley and serve.
Notes
Plan Ahead: keep in mind that the recipe calls for cooked chicken so plan ahead (or use this method). Lasagna Noodles: if you are wondering about using regular lasagna noodles (the kind that need to be boiled), you can definitely try it. I always use no-boil lasagna noodles and adapted the sauce ingredients to account for that fact so I can't guarantee how regular lasagna noodles will work. Parmesan Cheese: also, don't forget to reserve 1/4 cup of the Parmesan cheese for the top! Make Ahead: finally (I promise this is the last thing), this lasagna can be made ahead of time up to a day and refrigerated - just add about 15 minutes onto the covered baking time. It can also be frozen; bake for an hour and 15 minutes, uncover and bake 30-45 minutes until cooked through.