Herbed Feta and Steak Sandwich

Name: Herbed Feta and Steak Sandwich
Ingredients: 2 tablespoons Dijon or coarse, sharp mustard; 2 tablespoons Worcestershire sauce; 3 tablespoons olive oil, divided; 4 cloves garlic, smashed but not chopped; 2 teaspoons reduced sodium soy sauce; 1 1/2 pounds flank steak; 1/2 cup feta, crumbled; 3 tablespoons plain yogurt; 2 sprigs dill fronds, coarsely chopped; 3 or 4 chives, finely chopped (optional); 3 loosely-packed tablespoons coarsely chopped Italian parsley leaves; 1 tablespoon capers, lightly chopped, plus more to taste; Honey, to taste (optional); Four 6- to 8-inch slices of a standard baguette or a sourdough roll, sliced lengthwise; Stoneground mustard, to taste; 1 handful lettuce leaves or arugula; 8 slices ripe tomato; Salt and freshly ground pepper, to taste