Toast the cumin and coriander seeds in a dry pan until the fragrance is released. Remove them from the heat and grind finely in a pestle and mortar with the achiote seeds.
Chop the peppers, onion, spring onion and garlic finely. Combine with the ground spices, oregano and salt and pepper. Either use a blender or take some time with the pestle and mortar to get it as smooth as possible.