Heat butter in a skillet over medium-high heat. Add corn and cook until softened, about 4-5 minutes.
To prepare vinaigrette, mix vinegar, salt, basil, and oregano in a bowl. Slowly add olive oil, whisking vigorously to ensure vinaigrette is well-combined.
To serve, toss tuna, mozzarella, corn, cherry tomatoes, celery and green onion with vinaigrette.
