Blend the oil, green onions, cilantro, garlic, salt, lime juice, sour cream, and water until mostly smooth.
Toss enough sauce with the shredded cabbage to lightly coat it, creating the garlic cilantro lime slaw. Reserve the remaining sauce.
Pat the shrimp dry with paper towels.
Combine the chili powder, cumin, onion powder, garlic powder, cayenne, and salt.
Coat the shrimp evenly with the spice mixture.
Heat a drizzle of oil in a large skillet over medium-high heat.
Cook the shrimp for 5–8 minutes, turning occasionally until pink and fully cooked.
Warm the tortillas.
Spread mashed avocado onto each tortilla.
Top with the slaw, followed by the seasoned shrimp.
Finish the Spicy Shrimp Tacos with Cotija cheese, extra shrimp taco sauce, and fresh lime wedges.