Rinse the shrimp under running tap water and pat it dry with paper towels. In a large bowl using a mixer, whisk on low the flour, baking powder, oregano, mustard, egg, beer and granulated shrimp broth (you can use salt and pepper instead of the shrimp broth/bouillon). Whisk until there are no lumps left. The batter will be kind of runny, but it will stick to the shrimp, as long as you keep your ratio right (1 cup of flour, to 1 tbsp of baking powder, to one 12 oz. can of beer). Set aside and let it rest while oil is heating.
Pour oil in a deep frying pan or skillet and heat over medium-high heat. You can also use your deep fryer. In that case, pour enough oil and heat to 350 F until oil shimmers. It is important to achieve an even brown batter, so keep an eye on the battered shrimp so that they don't burn, just brown. Dip each shrimp into the batter and coat thoroughly. Once the oil is very hot fry the battered shrimp until evenly browned and cooked (3 - 4 minutes). Set a paper kitchen towel on a large plate to absorb excess grease. Keep warm.
Make the creamy Avocado-Cilantro-Jalapeno Sauce (you can make this the day before and just keep it refrigerated in an air-tight container) by processing in a blender avocado, cilantro, Jalapeno pepper, onion, mayo, lemon juice, water and salt and pepper to taste. Blend until smooth. Refrigerate any leftovers for up to 4 days.
Make the Pickled Cabbage by mixing in a bowl cabbage, radishes, tomatoes, lemon juice, vinegar (or pickled jalapeno juice), olive oil, dried oregano and salt and pepper. Have all your ingredients chopped/sliced/shredded in advance so by the time you are ready to serve the tacos you just dump garnish ingredients into a bowl and mix them. You can also prepare the pickled veggies the day before and keep them in the fridge, although the radishes will lose some of their color.
To assemble the tacos: Warm up the tortillas, place 4 - 5 shrimps per taco on the tortilla and top with garnish and dollop some sauce.
Notes
Peanut oil is the best oil for deep-frying due to the fact that it has a High Smoke point.