Coat a 9x13 ceramic baking dish with cooking spray.
Add the chicken, orzo, chicken stock, salt, and pepper, stirring until well combined.
Nestle the Boursin cheese into the middle of the dish and sprinkle the cherry tomatoes evenly over the top. Do not stir.
Cover with foil and bake for 30 minutes.
Add the spinach, and stir until everything is well combined. Bake for an additional 5-10 minutes, or until the orzo is completely cooked through.
Stir again and serve. The casserole will continue to set as it cools, so if it's still a bit liquidy, just let it sit for 5- 10 minutes before serving.
Notes
Oven Temp: Make sure your oven really is at 425°F, so your casserole cooks in just 30 minutes.
Check for Doneness: Give the orzo a little test-taste at 30 minutes, and pop it back in the oven for 5 minutes if it's not as chewy as you like.