Preheat oven to 375 degrees F. Coat two, 8-inch square baking dishes with cooking spray.

Halve squash lengthwise and scoop out the seeds. Place cut-side down on a microwave safe plate and add 2 tablespoons water. Microwave, uncovered, on high about 10-12 minutes or until the flesh can be scrapped with a fork but is still tender-crisp. Scrape the strands onto a plate and set aside.

Place broccoli in a microwave-safe dish, add 1 tablespoon water and cover. Microwave on high, stirring occasionally until just barely tender-crisp, 2 to 3 minutes. Drain and set aside to cool.

Meanwhile, heat oil in a large nonstick skillet over medium-high heat. Add mushrooms and cut-up uncooked chicken and cook, stirring for about 8-10 minutes. Add onion and continue cooking until the onion is tender and the mushrooms and chicken are lightly browned.

Stir in garlic, thyme and pepper, cook stirring for 30 seconds. Stir in soup (undiluted with water) and heat through. Stir in reserved spaghetti squash and broccoli, gently toss t combine well.

Divide the mixture between the prepared baking dishes and sprinkle each with ¼ cup cheddar cheese. Cover with foil. Label and freeze 1 casserole for up to one month.

Bake the remaining casserole until bubbling, about 25 minutes. Uncover and continue baking until lightly browned along the edges, 10 minutes more. Let stand for 5-10 minutes before serving.