Prep: Cook chicken with salt, pepper, and a little vinegar. Chop or shred as desired (this can be done a day or two in advance).
Heat oil, saute a sliced onion, add chopped mushrooms, mix well. Add cooked chicken, stir till well mixed. Add a dash of sweet Diana sauce, Sriracha (optional), and cook till dry.
Assembly: spread a little butter or may on a tortilla, add a fistful of arugula, a spoonful of chicken mix, a slice of havarti cheese. Wrap and toast all sides on a heated pan.