Heat the oil in a heavy, large pot over medium heat. Add the onions, potatoes, yams, garlic, tomatillos and poblanos. Cover and sweat until the onions are tender, stirring often to prevent browning, about 8 minutes. Mix in the oregano, flour, cumin, 1 teaspoon salt and 1/2 teaspoon pepper. Add the hominy with the juices and the broth and bring the chili to a simmer.