Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Use a cast iron skillet, if you have one.
Add bell peppers and onion; season with 1-1/2 tablespoons of the fajitas seasoning mix and cook for 5 minutes, or until tender, stirring frequently.
Remove vegetables from skillet and transfer to a plate; set aside.
In the same skillet, add the rest of the olive oil and shrimp; season with 1-1/2 tablespoons of the fajitas seasoning mix and cook for 2 to 3 minutes, or until pink.
Stir in the previously prepared veggies; continue to cook for about 30 seconds, or until everything is heated through.
Spoon prepared veggies and shrimp on warm whole wheat tortillas.
Optionally, top with cheese, sour cream and avocado.
Serve with lime.