In a large Dutch oven over medium-high, heat the oil until shimmering. Add the onion and cook until lightly browned, about 5 minutes. Add the garlic, ancho powder and cumin, then cook, stirring constantly, until fragrant, about 30 seconds. Add the tomatoes and cook, stirring, until most of the liquid has evaporated, 3 to 5 minutes. Add the broth and bring to a simmer. Stir in the chicken and hominy, then bring to a simmer. Reduce to medium, cover and cook until the chicken is opaque throughout, about 20 minutes.