Boil a pot of water. Shuck the corn and place into boiling water and boil for about 10-15 minutes, until tender. Add the peach slices to an oiled baking sheet and then drizzle with 1 tablespoon olive oil and sprinkle with salt. Roast for 15 minutes.
While the corn and peaches are cooking, add the arugula and spring mix lettuce to a large bowl with a lid or a gallon-sized bag and mix. Next, blend the dressing ingredients together in a small bowl.
Add the sliced red onion and watermelon to a large container with a lid and toss. Remove the peaches from the oven and toss them into the large container. Cut the corn from the cobb, laving some larger chunks of corn and then toss into the container and cover.
Right before serving the salad, toss together the lettuce mixture, corn/peach/watermelon mixture, and the dressing mixture. Sprinkle with more salt and pepper, if desired, and then garnish with avocado slices.
Notes
To travel with this salad, keep the spring mix/arugula mixture in one container or a gallon-sized bag, the corn/peach/watermelon mixture in a separate large bowl with a lid, the dressing in a covered jar, and the avocado whole or already sliced.