Bring a large pot of salted water to a boil. Cook the orzo according to package directions. Drain and reserve.
Heat a large sauté pan over medium-high heat. Add the oil, red pepper, green pepper, and yellow onion. Cook until softened (about 3 minutes).
Add the shrimp and sprinkle the Cajun seasoning over the contents of the pan. Continue to cook, stirring until the shrimp is just about cooked through (about 2 minutes).
Add the orzo and 2 – 4 TBSP water to deglaze the pan and cook the shrimp the rest of the way through. Stir well to coat the orzo. Serve immediately or let cool and serve at room temperature.