To make the dressing, in a small bowl whisk together the mustard, anchovy paste, Worcestershire sauce, lemon juice, salt and pepper. Drizzle in the oil and whisk in the Parm; set aside.
Add the escarole to a large bowl, top with the onions, mint and walnuts, and drizzle with some of the dressing. Gently toss everything together and dig in right away!