Heat a grill pan over high heat. Toss green onions with 1 teaspoon olive oil; sprinkle with 1/8 teaspoon kosher salt. Cook 2 minutes on each side. Chop onions; combine with fresh corn kernels and minced shallots. Stir in 1 tablespoon olive oil, lemon juice, vinegar, and 1/4 teaspoon kosher salt. Sprinkle with chopped fresh chives and chopped fresh tarragon.