Combine meat, onion, and garlic in a large skillet; cook over medium heat until meat is browned, stirring to crumble. Drain off pan drippings. Add tomato paste, 1 1/2 cups water, chili powder, and 1 teaspoon salt; reduce heat and simmer, uncovered, 15 minutes or until thickened, stirring occasionally.
Combine cornmeal and 1 cup water in a small bowl, stirring well; set aside. Bring remaining 5 cups water to a boil in a large Dutch oven; stir in 2 teaspoons salt and cornmeal mixture. Simmer, uncovered, 30 minutes, stirring often.
Spread half of cornmeal mixture in bottom of a lightly greased 12- x 8- x 2-inch baking dish. Spoon meat mixture over cornmeal mixture. Spread remaining cornmeal mixture evenly over meat mixture. Bake at 350° for 30 minutes or until firm.