Whisk together ¼ cup Dijon, 2 tablespoons brown sugar, 2 tablespoons Worcestershire, and 2 tablespoons oil in a large bowl. Season with salt and pepper.
Add 4 chicken breasts, toss to coat, then cover and refrigerate for 30 minutes, up to 2 hours.
Meanwhile, in a medium bowl, combine 2 large diced tomatoes, ½ cup red onion, 2 tablespoons minced jalapeño, 2 tablespoons minced cilantro, ½ teaspoon minced fresh garlic and 2 tablespoons lime juice; season with salt and pepper. Toss to combine and set aside.
Cook 4 strips diced bacon in a medium skillet over medium-high heat until crisp, about 10 minutes; transfer to a bowl to cool. Reserve drippings. Once cool, combine cooked bacon with 1 cup pepper Jack.
Preheat a grill to medium for 10 minutes, or heat a grill pan over medium. Brush grill grates or pan with bacon drippings (careful of any flare ups if cooking on grill). Remove chicken from marinade, letting excess drip off, and place on grill or pan. Cook, covered, until a thermometer inserted into the thickest part registers 165ºF, 5 minutes per side. Discard remaining marinade. Top chicken with bacon-cheese mixture, cover, and cook until cheese is melted, 1 minute more.
Serve chicken with pico de gallo.