CHIMICHURRI: PROCESS ingredients in food processor until almost smooth. Refrigerate, covered, until ready to use.
FOR each sandwich: Marinate 1 chicken breast in 1 oz. dressing for 1 hour. Remove from marinade; discard marinade. Grill chicken on medium heat until internal temperature registers 165ºF, turning after 4 min.
PLACE 1 oz. spinach, 1 tomato slice and grilled chicken breast on bottom half of pretzel roll. Top with 3 Tbsp. chimichurri and 1 Tbsp. mayo. Cover with top of bun.