Heat oil in a stick pot or Dutch oven over medium-high heat. Add onion and cook, stirring, for 5 minutes. Add garlic and cumin and cook, stirring, until fragrant, about 1 minute. Add the diced chiles, chicken stock, enchilada sauce, chicken, and hominy. Bring to a simmer, reduce heat, and let simmer for 5–10 minutes. Taste and add salt and pepper as needed.