Start by prepping your station and measuring out all your ingredients and spices.
In a hot pan, roast your garlic, onion, tomato, cinnamon stick, and chile guajillo. Turn them around until they’re nice and toasty on all sides. Be careful with the guajillo—if it burns, it'll turn bitter.
In a mortar, grind your spices. They don’t have to be super fine—a rough grind is just fine since everything will end up in the blender anyway.
Squeeze 1 cup of orange juice. If your oranges are sweet, balance it with 1/2 cup of lime juice. If your oranges are on the sour side, just stick with 1.5 cups of sour orange juice.
Add your roasted veggies, ground spices, and juices to the blender, along with the star of the show—the Achiote. Add an extra 1/2 cup of water to the blender.
Once your marinade is ready, pour it over the meat in a bowl. Use just enough to fully cover the meat, and save the rest in a separate container in the fridge.
Cover the bowl and let the meat marinate in the fridge overnight.