Peel the shrimp and pat dry with paper towels. Place in a small bowl.
Seed and slice the peppers into strips. Place them in a separate bowl.
Slice onion in half from top to bottom. Peel outside layer, then slice. Place them in to bowl with the peppers.
Whisk the marinade up again and pour half on the shrimp and the other half on the peppers and onions. Toss to coat.
Preheat a cast iron skillet over MEDIUM heat. Add 1-1/2 teaspoons of olive oil and brush bottom to coat. Add the shrimp in a single layer. Cook for about 2 minutes, then flip for another 1-2 minutes. Shrimp should be opaque and firm. DO NOT OVERCOOK. Time may vary due to size of shrimp used in recipe. Remove to a dish immediately.
Place the remaining oil (1-1/2 t) in the skillet with the remaining peppers and onions. Strir frequently over MEDIUM heat until softened and a little charred, 8-10 minutes. Take the skillet off of the heat.
Add in the reserved shrimp with any juices back into the skillet. Sprinkle the cilantro over the ingredients and drizzle over a half of a lime juiced. Gently toss to combine.
In the middle of the warmed tortilla, place a few of the veggies. Layer 4-5 shrimp on top of that, then drizzle the fajita dressing over the top. Fold and devour!