For the shrimp: Whisk the cumin, chili powder, paprika, garlic powder, oregano, salt, pepper and cayenne together in a small bowl.
Place the shrimp in a medium bowl and sprinkle with the spice mixture. Toss to coat. Set aside for 10 minutes.
Meanwhile, for the avocado sauce: Combine the avocados, scallions, garlic, lime zest and juice, jalapeno, cilantro, water, vinegar, cumin and salt in a blender. Blend on high for 2 minutes or until a smooth, creamy sauce forms, stopping and scraping down the sides as needed.
Char the tortillas by holding them with tongs over an open flame until they’re warmed and browned in spots. Transfer them to a plate as they’re done; cover the tortillas with foil and keep warm.
Heat a large cast-iron skillet over medium-high heat. Lightly spray with oil to prevent sticking. Working in batches, cook the shrimp 1 to 2 minutes per side or until firm and cooked through.
To serve, place 2 tortillas on a plate and top with some shredded cabbage followed by about 5 shrimp per taco, a drizzle of the avocado sauce, diced tomatoes and hot sauce if using. Repeat with the remaining tortillas, shrimp and fillings. Serve with lime wedges.