In a large bowl, whisk together the vinegar and mustard. Using a lint-free kitchen towel, lightly press the tofu to extract some of the moisture. Cut the pressed tofu into 1/2-inch cubes and add it to the bowl. Add the grapes, celery, pecans, avocado, and poppy seeds. Gently toss to combine. Serve on whole grain bread or over a bed of greens.