Bring a large pot of lightly salted water to a boil over high heat. Add the orzo pasta, and cook until al dente, 6 to 7 minutes; drain.
Heat the olive oil in a large skillet over medium-high heat. Add the mushrooms, and season with onion powder, salt, and pepper. Cook and stir until the mushrooms have softened and released their liquid, about 5 minutes. Stir in the butter, corn, peas, parsley, and cooked orzo pasta. Season to taste with salt and pepper, and serve immediately.