Preheat oven to 350. Spray 9x13-nch pan with cooking spray.
Bring 1-1/4 cups chicken stock to a boil. Meanwhile whisk together 1 cup cold water and cornmeal until smooth. Gradually add water/cornmeal mixture to boiling water, whisking constantly. Continue whisking until mixture is fairly thick and all lumps are gone. Spread polenta mixture into bottom of prepared pan and set aside.
In a Dutch oven, brown turkey, onion and garlic over medium-high heat until turkey is no longer pink. Add chili powder and next 7 ingredients (through corn); mix until thoroughly combined. Spread turkey mixture over polenta crust and bake for 20-25 minutes.