For the Dressing
Whisk first 4 ingredients in a medium bowl to blend. Gradually whisk in oil. Season with salt and pepper. Can be made 1 day ahead, cover and refrigerate.
For the Salsa
Preheat oven to 400 degrees F. Roast corn for 12 minutes. Cool. Cut corn from cob. Transfer corn to large bowl, Add tomatoes, onion, and cilantro; mix. Can be made 6 hours ahead. Cover and chill.
For the Steak
Combine first 4 ingredients in a small bowl, Spread spice paste over both sides of steak. Cover and refrigerate at least 2 hours (and up to 6 hours).
Prepare barbecue (medium high heat). Grill steaks to desired doneness (about 5 minutes on each side). Transfer steaks to cutting board and let stand 5 minutes.
Meanwhile, add avocado and 2 tablespoons dressing to salsa and mix. Season to taste with salt and pepper. Place greens in large bowl and toss with enough dressing to coat. Fan some nectarine slices on outer edge of salad. Top each salad with 1/2 cup salsa.