Preheat oven to 375°F (190°C). Line a baking dish with parchment paper (optional).
Prepare the peppers: Wash and cut them in half, removing seeds.
Bake the peppers in a lined baking dish for 30 minutes at 400.
Cook the chicken: You can poach the chicken breasts in simmering water until cooked through. Shred the chicken using two forks or put the chicken in the crockpot with 1 cup of water and cook on high for 3 hours before shredding.
In a large bowl, mix the shredded chicken, BBQ sauce, garlic, salt, and pepper. Adjust seasonings to your taste.
Spoon the filling generously into each pepper half.
Top with a sprinkle of dairy-free cheese, if using.
Bake and serve: Arrange the stuffed peppers in the prepared baking dish. Bake for 20-25 minutes, or until the filling is bubbly and heated through. Let cool slightly before serving.