Dab shrimp with paper towels to help dry some of the excess moisture, place in a medium mixing bowl.
Add in lime juice, chili powder, cumin, coriander, and cayenne pepper and toss, set aside.
Heat 1 1/2 Tbsp olive oil in a 12-inch cast iron pan or non-stick skillet.
Add in onions and saute 2 minutes then add in bell peppers, season with salt and pepper and saute until crisp tender, about 5 - 7 minutes longer.
Transfer peppers to a sheet of foil and wrap to keep warm. Return skillet to heat and add in remaining olive oil.
Season shrimp with salt and pepper (about 1/2 tsp of each) and toss, add to skillet and cook 1 1/2 minutes.
Add garlic to skillet and toss, then cook shrimp through, about 1 - 2 minutes longer.
Toss in cilantro then serve filling over tortillas along with avocado slices and queso fresco if desired.
*I left the tails for pictures just because I think they look better, but I do recommend removing tails.
**I used 2/3 of a red, yellow and green to equal 2 peppers.