In a large stock pot, bring enough water to a boil to cook a pound of pasta. (Check the instructions on the box for exact amount. Make ssure to use enough water.) When the water comes to a roaring boil, add salt, throw in the pasta, and give it a stir. Cook for the time listed on the box. When done, drain and rinse with cold water.
While the pasta is cooking, heat a large skillet over medium heat. Add two tablespoons of oil oil. Then add in the bell peppers and diced onions. Cook until soft and tender, about 5 to 7 minutes, stirring often. (see note 2)
Whisk together the ingredients for the dressing, making sure to break up the fajita seasoning and fully incorporate it into the liquid.
In a large bowl combine all of the ingredients. The pasta and cold shrimp will bring down the temperature of the sauted vegetables and it can be sserved at room temperature. If you would like to make this ahead of time, refergerate (covered) and then allow it to sit out for at leasst 15 minutes before serving.