Mix the paprika, ancho chili powder, cumin, sugar and salt together in a large bowl. Add the shrimp to the spices and toss to coat evenly. Set aside.
Melt the butter over medium heat in a 12-inch skillet. Add the garlic and cook, stirring with a wooden spoon, for one minute. Do not brown. Add the shrimp and continue cooking over medium heat, stirring frequently, until the shrimp are almost cooked but still opaque in spots, 3 to 4 minutes. Add the Worcestershire sauce, lemon juice and water and cook until shrimp are done, 1 to 2 minutes more. Scatter the scallions over top and serve.
