Serve this dish with taco toppings (such as salsa, chile and bell peppers, radishes, and shredded lettuce) that can be sprinkled over each serving.
1. Place oven rack in top position, and preheat oven to 425°F. Coat 9-inch pie dish with cooking spray. Whisk reserved bean liquid with tomato paste in bowl.
2. Heat oil in large skillet over medium-high heat. Add 2 cups onion. Cover, and cook 4 minutes, or until onion begins to soften, stirring occasionally. Add chili powder, and stir 10 seconds to coat onions. Stir in tomato paste mixture, 1 cup tomatoes, and then beans. Bring to simmer, stirring occasionally. Reduce heat to low, and simmer uncovered, 6 minutes, or until flavors blend and chili liquids thicken. Season with salt and pepper, if desired.
3. Meanwhile, combine cornbread mix, 1/3 cup yogurt, egg, sugar, and 1 Tbs. water in medium bowl.
4. Spread chili beans in prepared pie dish. Pour cornbread batter over beans, spreading with back of spoon. Bake 10 minutes, or until cornbread is set and golden.
5. Meanwhile, finely chop remaining 1/2 cup onion. Place in small bowl; mix in remaining 1/2 cup tomatoes, and season with salt and pepper, if desired.
6. Divide shepherd’s pie among shallow bowls. Serve with tomato salsa and remaining 1 cup yogurt.