Cut the head of the shrimps and peel off. Take the shrimp into a perforated bowl and wash with cold water.
Drain excess water and cut the shrimp into pieces (about 1 inch). Keep the cut shrimps in another bowl.
Sprinkle old bay seasoning and onion powder over the shrimps. Stir for absorb and set aside.
Heat a skillet with olive oil on medium-low. Add half of the chopped onion, cube cut tomatoes, and cilantro, cook for 1-2 minutes.
Then add the shrimp and mix them very well. Cook for 5-7 minutes or until the shrimps turn orange. Stir occasionally to avoid burning. Remove from heat and set aside.
Heat another deep skillet with canola oil to fry tortillas. Wait for 1 minute to heat the oil. Place tortilla into heat up oil (one at a time). Seethe for about 30 seconds or less until the tortilla is soft enough to fold.
For making a taco shell, fold the tortilla. Flip the tortilla occasionally to impede over frying. Once the tortilla is done frying, arrange it onto a plate.
Put a paper towel on the plate so it can soak excess oil. Fry all tortillas in the same way.
Then make guacamole. To make guacamole add avocado, shredded green onion, lime juice, onion powder, salt, and the rest of the chopped onion, cilantro and cube cut tomatoes in a bowl. Grind them with a hand grinder until smooth.
Put the guacamole, fried shrimp, and sour cream into the taco shells and keep them on a plate. Top with shredded Mexican cheese.
Garnish with cilantro and serve with salsa.