In a small bowl, stir together the fajita seasoning ingredients.
In a large bowl, add the shrimp, two tablespoons of olive oil, the juice from half a lime, and the fajita seasoning. Toss it all together until the shrimp is well coated and set it aside to marinate.
Heat two tablespoons of olive oil in a large skillet over medium heat. Add the bell peppers and onions, and saute for 4-5 minutes or until softened and the onions have started to caramelize. Transfer to a plate.
In the same skillet, add the shrimp and cook for about 2-3 minutes on each side or until they turn pink.
Add the bell peppers and onions back into the skillet, give everything a toss, and squeeze more lime juice on top. Serve immediately with tortillas and extra toppings such as sour cream, pico de gallo and guacamole.