1. In a small skillet with a lid, bring 1 inch salted water to a boil. Add chicken. Cover, and cook over medium-low heat, 5 minutes. Remove from heat, and let steam, still covered, until cooked through, 10 to 12 minutes; remove chicken. When cool enough to handle, thinly slice crosswise.
2. While chicken is cooking, stir together mayonnaise, shallot (if using), mustard, vinegar, and thyme in a medium bowl; season with salt and pepper. Add chicken, and toss to coat.
3. Lay sandwich wraps on a work surface. Leaving a 1-inch border all around, layer with cheese, spinach, then chicken mixture.
4. Fold in sides by about 1 inch, then roll up tightly from the bottom. Wrap each tightly in plastic or waxed paper. Refrigerate up to 1 day.
