In a bowl, combine mayonnaise, vinegar, honey, poppy seeds, salt and pepper. Refrigerate until ready to dress the salad. This can be prepared up to 2 days ahead.
Preheat oven to 375°F Place the chicken breasts in one layer in a baking dish and season with salt and pepper. Add to the pan 1/2 cup water. Cover with foil and bake 25 minutes until completely cooked through. Remove cooked chicken breasts from pan, cool at room temperature. Note: I find mixing the ingredients together while still slighly warm absorbs the flavors better.
When the chicken is cool, dice into bite-size chunks and transfer to a large bowl. Stir in pecans, grapes, celery and dressing.