Place the oil in a large deep nonstick skillet and preheat over medium-high heat. Add the zucchini, corn, red bell pepper, onion, and oregano. Cook, stirring frequently, for 3 to 4 minutes, just until the vegetables are crisp-tender. Periodically place a lid over the skillet if it becomes too dry. (The steam released from the cooking vegetables will moisten the skillet.)
Add the rice and salt to the skillet mixture and reduce the heat to medium. Cook, stirring frequently, for a couple of minutes, until the mixture is heated through. Add a tablespoon or two of water if the mixture seems too dry. Serve hot.