This is *not* the bang bang sauce from Cheesecake Factory -- a calorie-bomb of coconut curry and peanut sauce (I mean, it probably tastes amazing).
This is the Laotian Bang Bang sauce -- a funky, fiery, sweet/tangy/spicy mix. Ie: a slow cooker friend.
In my experience, the best slow cooker recipes are deeply, aggressively flavored (see also this miso ginger garlic chicken). Slow cookers get a bad reputation because they remind people of dull stewy mush.
But that's why you fight against the murky "brown" flavor with brightness. In Laotian cuisine, bang bang is typically eaten with sticky rice (the way fries are eaten with ketchup). The same idea applies here: you want to match a tender, blank-slate food (slow-cooked chicken, sticky rice), with something that awakens the palate. Now you have the best of both worlds -- something soft and pillowy with something sharp and vibrant.
My preparation includes two ingredients that aren't in classic bang bang sauce: gochujang and black bean sauce. I did this because slow-cooker sauces need to be thick. They'll get watered down a lot as the chicken cooks (such are modern chickens, very watery). Both sauces are thick, fermented and funky, and serve as the foundation for the more ephemeral top notes of this dish (ginger, lime, etc).
So, to review: Laotian bang bang: wakes you up. Cheesecake Factory bang bag: knock you out.
Skin an entire whole chicken (I do this because the fat doesn't have anywhere to go in a slow cooker. Since the slow-cooker is a pro at keeping meat tender, don't worry about going skinless!).
In a small bowl, mix 2 tablespoons gochujang, 2 tablespoons of black bean sauce, 1 teaspoon chopped chili peppers (Thai chilis, piri-piri, whatever you have), 5 cloves of chopped garlic, 2 tablespoons chopped ginger, 1 tablespoon chili oil, 1 chopped lemongrass stalk (or 1/2 teaspoon of dried lemongrass), 1 tablespoon palm sugar, 1 teaspoon fish sauce, 1 pinch of dried ginger, 1 pinch of dried galangal (or just more ginger if you can't get this), 1 pinch of cardamom. Add enough water to mix, but not too much.
Place chicken in slow cooker and pour sauce over chicken, making sure to get every crevice. Add one diced lime. Cover and cook on low for 7 hours. Serve with sticky rice and Thai basil.