Prick sides of spaghetti squash with fork and bake on a cookie sheet whole for 60 to 75 minutes at 375 degrees or until you can press the flesh in with an oven mitt covered hand. Cool for 10 minutes and then cut in half and remove seeds and pull the spaghetti with a fork down to the rind of the squash. Set aside.
Cook chicken breasts and dice in small pieces or cook ground chicken and drain, whichever you prefer. Set aside
In a large pot, melt butter, add garlic and then spinach to wilt. I cut the spinach as it's cooking with kitchen shears to make it easier to stir in with the squash
Add cream cheese, heavy whipping cream (or half n half), parmesan, salt and pepper and red pepper flakes to taste
Mix in squash and chicken and stir until well combined
Add a handful of mozzarella cheese (1/4 cup or so) and stir well
Pour into a 9x13 pan and cover with remaining mozzarella cheese
Bake at 400 degrees for 35 minutes and let cool for 5 to 10 minutes to help sauce thicken up before serving