Season the chicken thighs well with BBQ rub. Preheat your grill to medium-high heat, then cook the chicken for about 6–7 minutes on each side until it reaches 165°F inside. Let it rest for a few minutes before chopping into bite-sized pieces so the juices stay inside.
While the chicken is grilling, fry the bacon strips in a hot pan until golden and crispy. Place them on paper towels to drain excess grease, then chop into small pieces.
Lay shredded lettuce on a large cutting board, then add chopped chicken, crispy bacon, and tomato slices. Use your knife to chop everything together so the flavors mix evenly.
Sprinkle shredded mozzarella over the mixture, then drizzle with ranch dressing. Add salt and pepper to taste, then chop again so every bite gets cheesy, creamy goodness.
Lightly toast the sub rolls to give them crunch and sturdiness. Pile the chopped filling generously into each roll and serve while warm and melty.