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.
To make the plantain dough
Grate the green plantains finely into a mixing bowl.
Add 2 tablespoons of achiote oil, ½ cup of unsweetened peanut butter, the 2 tablespoons of mixture you reserved earlier, a handful of finely chopped cilantro, 2 tsp dried oregano, 1½ tsp of salt, and ½ tsp pepper.
Now the kneading starts! Press all the ingredients together until smooth. Make sure the dough is wet, but not runny; it has to hold together. If it becomes dry, slowly add water.
Assembly and frying
Make sure your hands are wet and keep a bowl with water nearby to re-moisten your hands when needed.
Once the dough is ready take a handful of dough and make it into a ball. Flatten into a disc about the size of your palm. Make a dent in the middle of the disc and add about a Tbsp of the shrimp and peanut butter stuffing.
Close the dough over the filling, and shape the corviche into an oval. If the ovals crack, make your hands more wet and smooth out the surface.
Fry the corviches in medium-high heat oil for 10-15 minutes until dark brown.
For serving
Split open the corviche lengthwise. Be careful they retain the heat well! Pour some of the extra filling over the split. Add pickled onions and drizzle mayo over it all. Enjoy!