Clean and devein the shrimp.
Heat oil in a pan over medium heat. Add onion and cook until softened.
Add the shrimp, Old Bay seasoning, and onion powder to the pan. Cook for 5–7 minutes or until pink in color.
In another pan over medium heat, heat the tortillas until lightly golden.
Assemble tacos by adding shrimp mix, cheese, sour cream, salsa, cilantro, and green onion into each taco. Serve with diced tomatoes and wedges of lime.
Slice avocado and add to tacos as desired.