Place the edamame, corn, scallion, garlic, olive oil, salt and pepper into a 13 by 9 metal pan and stir to combine. Place on the middle rack of the oven and roast for 10 to 15 minutes, just until the edamame begins to brown. Remove from the oven and place in the refrigerator until completely cool, approximately 30 minutes.
Add the tomato, basil and vinegar to the edamame mixture and toss to combine. Taste and adjust seasoning, as desired. Serve chilled or at room temperature.