Heat the oil in a heavy skillet over high heat.
Throw in the shrimp and cook, tossing it around, until opaque, 2 to 3 minutes.
Reduce the heat to low and pour in the tomato or enchilada sauce, stirring to combine.
Stir in the cumin and cook for another 1 to 2 minutes. Add the butter, then remove it from the heat.
Serve with warm tortillas stuffed with shrimp and topped with mixed cabbage, pico de gallo, avocado slices, and cilantro. You can serve with a wedge of lime to squeeze on before eating.