Preheat oven to 400 degrees. Roast corn for 10 minutes, allow to cool slightly, then use a knife to remove all the kernels, reserve. In a cast-iron skillet, heat olive oil until the first whisps of smoke appear. Add onion and sauté 2 minutes. Then add peppers, green beans, corn, and garlic, and cook for 5 minutes, until all vegetables are tender but still have a little bit of crunch. Remove from heat, add tomatoes and parsley, and toss to combine.