1- Mix together the ancho chilies, cumin seeds, coriander seeds, mustard seeds, and black peppercorns, and cook on a sheet pan in a 350 degree oven until toasted. Let cool completely.
2- In a spice grinder, add chili/seed mix to the thyme leaves, salt, onion powder, and garlic powder. Grind together into a fine powder.
3- Combine the fine powder with the canola oil and mix well.
4- Rub entire roast with the oil/ spice blend. Meanwhile, preheat oven to 320 degrees.
5- Sear all sides of the exterior of the roast in a frying pan. Note, the spice mixture will blacken. This is ok.
6- Finish cooking the roast in the preheated oven until it reaches an internal temperature of 140 degrees at the center. Allow to rest for a full 12 minutes before slicing.