Cut corn kernels off cob and place kernels in a large mixing bowl. Add edamame, black-eyed peas, red onion, celery, and butter or oil. Toss until combined. Add balsamic vinaigrette and minced garlic, mix well. Add salt and pepper, to taste. Refrigerate until ready to serve.
Mix red leaf lettuce with baby spinach and line a serving bowl or platter with lettuce and spoon salad over the bed of lettuce. Arrange sliced plum tomatoes around the edge of the dish, if desired, and serve.