Preheat your oven to 400 degrees F.
Place the squash and onions in a 13”x9” baking dish, pour the oil over them, and roast in the oven for 20 minutes.
When the squash has about 10 minutes left in the over-- whisk all the sauce ingredients for 7-9 minutes over medium. It should thicken up. If it doesn't add flour by the teaspoon, mixing thoroughly in between, until it does. Be sure to constantly stir this mixture so it doesn’t burn.
Remove the squash and onions from the oven, add the spinach and cranberries and mix together.
Pour the finished sauce over the squash base and toss everything together.
Sprinkle the breadcrumbs over the top and cook for another 8-12 minutes or until your squash is tender and all everything is heated through.
Serve and enjoy!