Preheat the oven to 350°F.
Place the spaghetti squash on a baking sheet (cut side down); pierce the rind with a fork in multiple places.
Add 1/2 cup water to the baking sheet.
Bake for 30-40 minutes or until the rind is soft.
Place the onion in the bottom of the slow cooker; layer the chicken over the onions; spread the mushrooms on top.
In a bowl, mix the tomato paste, spices, and water; pour over mushrooms.
Cover; cook on low for 4-4.5 hour or high for 2.5 hours.
Stir once or twice to break up the chicken.
Serve over spaghetti squash.