In a small bowl, mix together the Worcestershire sauce, brown sugar, mustard, 2 teaspoons salt, 1 teaspoon pepper, garlic and shallots. Gradually whisk in 1/4 cup vegetable oil until emulsified. Place the steak in a plastic zip-top bag. Pour the marinade over the steak and seal the bag. Marinate for at least 1 hour at room temperature or refrigerate overnight. Allow the steak to come to room temperature before cooking.
When ready to cook, preheat the broiler and set the oven rack at the highest point, as close to the flame as it can get and still fit the steak below. Fit a wire rack onto a baking sheet.
Place the marinated steak on the prepared baking sheet (or a broiler pan), sprinkle with salt and pepper and place it under the broiler. Cook for 3 minutes on the first side. Flip and cook for another 3 minutes for medium-rare. Remove from the oven and allow to rest 10 minutes. Slice thin strips of steak against the grain.
For the vinaigrette:
While the steak is resting, in a small mixing bowl, make the vinaigrette. Combine the vinegar, shallots, mustard and garlic and whisk in the oil. Season with salt and pepper.
For the salad:
Preheat a cast-iron grill pan over medium-high heat. Place the grape bunches on the grill to char, just until blistered, 3 to 4 minutes.
In a large bowl, add the greens and lightly dress the salad with the vinaigrette. Toss to combine.
For serving, pile the salad onto a plate and top with crumbled blue cheese and toasted pecans. Surround the salad with the sliced steak and grilled grapes.