Begin by preparing the fish head broth. Combine all the ingredients in a pot and add enough water to cover the ingredients by 1-inch. Bring to a boil. Simmer for 20 minutes or until the fish head is fully cooked. Turn the heat off and set aside to cool slightly. Strain and discard any solids.
While the fish head broth is cooking peel and devein the shrimp. Keep shrimp shells in a bowl and set aside. Clean the shrimp under cold water, place in a separate bowl and set aside.
In a medium saute pan melt 1 tablespoon of the butter over medium-high heat. Add the shrimp shells and paprika, saute for 3 minutes. Add the chopped tomatoes and beer and cook for 5 minutes more.
Transfer the shrimp shell mixture to a blender or food processor. Puree until smooth and pass mixture through a fine sieve into a bowl. Add the green plantains to the blender with 6 cups of drained fish head broth and puree until smooth. Strain into the same bowl as the shrimp broth.
In a Dutch oven or large pot heat the remaining 1 tablespoon of butter and achiote oil. Saute the red onion, green bell pepper, garlic, and cilantro for 3 minutes on medium high. Add the panela and cumin, salt and pepper, to taste. Cook, stirring, for another 3 minutes. Add in the cleaned shrimp and saute for 3-5 minutes.
Pour in the plantain and shrimp broth. Stir to combine and cook for until thickened, 5 to 7 minutes. Taste and season with additional salt and pepper, as needed.
For garnishing the soup, toss the thinly sliced red onion with the lime juice and 1 teaspoon salt. Mix to combine. Top each bowl of soup with a bit of the pickled red onions and some chopped cilantro.