This recipe is a spin on tacos—but much heartier and easier to serve. You can make your own Mexican seasoning by combining 1/2 tsp. chili powder, 1/4 tsp. cumin, 1/4 tsp. paprika, 1/4 tsp. cayenne pepper, and 1/4 tsp. salt. Prepare the mix in larger batches, and keep in an airtight container, ready to go.
Position broiling pan, or rack if using electric oven, 3 inches from heat, and turn broiler to high. Spray polenta slices with cooking spray, and place on broiling pan or baking sheet. Broil 5 minutes per side, or until browned.
Meanwhile, heat oil in large skillet over medium-high heat. Add onion, and cook 4 minutes, or until softened. Stir in lime juice, spice seasoning, garlic, and lime zest. Cook 4 minutes, or until onion is lightly browned. Add kidney beans and tomatoes; simmer 5 minutes, or until heated through.
Place 3 polenta slices on each plate, ladle bean mixture over top, and sprinkle with queso fresco and cilantro. Serve with sour cream, if desired.