Add the olive oil and onion to a medium skillet over medium heat. Cook until the onion is translucent and soft, about 8 minutes. Remove from the heat and let the onion cool.
Cook the orzo according to the package directions.
Grill or boil the corn until cooked and tender, about 5 minutes. Cut the kernels from the cobs.
Mix together the onions, orzo, cherry tomatoes and corn in a large bowl. Gently fold in the arugula. Drizzle with lemon oil and sprinkle the Parmesan on top.
You can prepare the salad in advance and add the arugula, lemon oil and Parmesan just before serving.