On a baking sheet, place the ancho chiles in a single layer. Toast in the oven for 5 to 7 minutes, or until they become fragrant and slightly darkened in color.
In a small pan, dry roast the cumin and coriander seeds over medium heat until fragrant and slightly browned, about 2 to 3 minutes.
In a spice grinder or a coffee grinder, grind the toasted ancho chiles, oregano, roasted cumin and coriander seeds, garlic powder, and onion powder to a fine powder.
Store the ancho chile powder in an airtight container in a cool, dark place for up to 6 months.