Preheat grill. Brush steak and corn with oil and season with salt and pepper and place on grill. Grill steak/corn about 6-8 minutes per side over medium heat. Cook longer if you like your meat more well-done. Corn will take about 10-15 minutes, rotating every 5 minutes. Remove the meat and corn and let it rest.
Add the peach quarters and onion halves onto the grill and grill for a few minutes to get grill marks and to slghtly carmalize.
Arrange the greens on a large serving platter. Cut the kernals off the corn and add onto the platter, along with the tomatoes.
Remove the peaches and onions from the grill. Quarter the onion and peaches and add to the salad.
Slice the steak into fine strips and lay on top of the platter.
Place all dressing ingredients into a jar with a lid and shake. Pour over the salad and give it a gentle toss.