Thinly slice the green cabbage. Thinly slice the red onion and place it in a bowl with cold water (this removes a bit of the strong onion flavor); drain before serving.
Mince the garlic. Pat the shrimp dry. In a medium bowl, mix the shrimp with the Old Bay seasoning, cumin, salt, and garlic.
In a large skillet, heat the butter on medium high heat. Cook the shrimp for 1 to 2 minutes per side until opaque and cooked through, turning them with tongs. Spritz with juice of the two lime wedges.
If desired, char the tortillas by placing them on an open gas flame on medium for a few seconds per side, flipping with tongs, until they are slightly blackened and warm. (See How to Warm Tortillas.)
To serve, place the cabbage and red onion in a tortilla, then top with shrimp. Squeeze with the juice of 2 lime wedges, then top with the taco sauce. Serve immediately.