Place chicken breast(s) in a saucepan and cover with water. Add rosemary, salt, pepper, bay leaf, garlic, onion and lemon juice.
Cover the saucepan with a lid and put it on the stovetop over medium heat. Bring to a simmer and lower heat to medium-low. Simmer until the chicken reaches an internal temperature of 160℉, about 6-10 minutes, depending on the size of the breast(s).
Remove chicken from water and allow it to cool.* Cut it into thin slices.
Lay out a wrap on a flat surface. Line ¼ of chicken slices across the wrap, slightly off circle to allow room for rolling. Top with ¼ cup guacamole, several tomato slices and ¼ cup baby spinach leaves.
Roll the wrap to form the sandwich (see hack below) and serve immediately. Store any leftovers in the fridge and assemble wraps as needed.
*At this point, the chicken can be stored in the refrigerator for up to 5 days or frozen for up to 4 months.