Preheat oven to 350F. Spray an 8x8 baking dish with cooking spray.

Bring a pot of salted water to a boil. Add spaghetti and cook 1 minute less than package directions, or until just under al dente, stirring occasionally. Drain and place in baking dish.

Heat butter in a skillet over medium heat. Add flour and stir to combine. Cook until golden, about 2-3 minutes.

Slowly add milk, stirring to combine. Reduce heat to medium-low and simmer until thickened, about 3-5 minutes.

Add broth and ½ cup parmesan and stir to combine.

Add sauce and chicken to baking dish and stir to combine. Top with ¼ cup parmesan and bake until top is golden brown, about 45-60 minutes.