Mix the ground coffee, brown sugar, smoked paprika, chili powder, salt, and black pepper in a small bowl. Rub this mixture all over the chicken thighs.
Place the rubbed chicken in the slow cooker. Add the diced onion, minced garlic, black beans, diced tomatoes, and BBQ sauce. Stir gently to combine.
Cover and cook on low for 6 hours or high for 3 hours until the chicken is tender.
Shred the chicken directly in the slow cooker with two forks and stir to mix with the sauce.
While the chili finishes, preheat the oven to 400°F. Whisk together the cornmeal, flour, baking powder, and salt in a bowl.
Stir in the egg, milk, and melted butter until just combined. Pour into a greased 8-inch pan.
Bake the cornbread for 20 minutes until golden on top. Cut into squares and serve alongside the chili.