Preheat oven to 375° F.
Heat oil in a 10-inch cast-iron (or ovenproof) skillet over medium-high heat.
Add onion, bell pepper, and turkey; cook, stirring frequently, for 6 to 8 minutes, or until turkey is cooked through.
Add tomatoes, tomato paste, chili powder, cumin, and ¼ tsp. salt. Bring to a boil, stirring frequently. Reduce heat to medium; cook, stirring frequently, for 10 to 15 minutes, or until sauce has thickened. Remove from heat. Coat sides of pan with spray.
While turkey mixture is cooking, boil water in medium saucepan over high heat.
Add cornmeal; cook, stirring constantly, for 2 to 3 minutes, or until cornmeal has thickened. Remove from heat.
Add remaining ½ tsp. salt, cheese, jalapenos (if desired), and corn; mix well. Spread evenly over turkey mixture.
Bake for 40 to 45 minutes, or until top is golden brown and turkey mixture is bubbling. Let sit for 10 minutes before serving.