Prepare the salsa and place in the refrigerator to chill.
Place a large skillet over medium heat and add the olive oil.
Add the diced onion and cook, stirring frequently, until the onions begin to soften. Add the shrimp, chili powder, cayenne pepper and salt.
Add the water and continue cooking for about 7 – 10 minutes over medium heat until the shrimp are cooked through. Remove from the heat, let cool and then refrigerate.
While the shrimp is cooling, slice the lettuce, drain and rinse the black beans, slice the tomatoes and shred the cheese.
When ready to assemble, place the broken taco shells in the bottom of a large bowl. Top with the lettuce and then the black beans. Arrange the tomato wedges around the edges.
Top with the cooled shrimp mixture, with the green onion and shredded cheese over the top.
Spoon the sour cream and salsa on top and serve.
