Whisk together the yogurt, 2 tablespoons of the olive oil, 2 tablespoons of the mustard, ½ teaspoon of the salt, and the pepper; set aside.
For the Salad:
Combine shrimp, 1 tablespoon of the remaining olive oil and remaining 1 tablespoon mustard in a large resealable bag; toss to coat and refrigerate for 1 hour.
Heat remaining 1 tablespoon olive oil in a large skillet over medium heat. Add corn to pan and cook, stirring occasionally for about 10 minutes. Remove corn to a serving bowl.
Increase heat to high and add shrimp to skillet; sprinkle with remaining ¼ teaspoon salt. Cook 2 to 3 minutes per side or until cooked through; transfer to bowl with corn. Cool 10 minutes.
Add radishes and lettuce to serving bowl and drizzle with prepared dressing. Toss to combine and serve immediately.