Sautée the red onion, green bell pepper, green onion stalk, and garlic in a pan with the cumin, 2 tsp dried oregano, salt, pepper and 2 tablespoons of achiote oil until the vegetables reduce almost to an orange paste.
At this point, remove 2 tablespoons of this mixture and set it aside for later.
Add 1 cup of raw unsweetened peanut butter to the pan. Add ½ cup of water to help the ingredients combine, and stir well.
Add the shrimp and cook for another 2 minutes before removing from heat. Add a handful of finely chopped cilantro and set to the side.