How to Make It
Process parsley, lemon juice, Dijon, garlic, 1 1/2 teaspoons of the salt, and 1 teaspoon of the pepper in a food processor until well combined, about 1 minute. While food processor is running, slowly add 2/3 cup of the extra-virgin olive oil. Transfer lemony-herb dressing to a jar with lid; set aside. (The dressing can be made ahead and stored in refrigerator up to a week.)
Preheat a grill pan or outdoor grill to medium-high (400°F to 450°F). Sprinkle chicken thighs with 1 teaspoon each of the salt and pepper. Toss garlic scapes and corn with remaining 1 tablespoon olive oil.
Grill scapes on preheated grill until tender and grill marks appear, 5 to 7 minutes. Grill corn, rotating, until grill marks appear, 8 to 10 minutes. Once corn is cool enough to handle, cut corn from the cob, and cut scapes into 1-inch pieces. Combine corn, scapes, tomatoes, and cucumber in a large bowl. Toss with mint, 1/3 cup of the lemony-herb dressing, and remaining 1/2 teaspoon salt and 1 teaspoon pepper.
Grill chicken thighs on oiled grates 5 minutes per side, and then flip continuously until a thermometer inserted in thickest portion registers 165°F, about 5 more minutes. Drizzle each chicken thigh with 1 tablespoon of the dressing; serve with the salad.