Drain the black beans, but reserve the liquid. Mince or grate the garlic. Peel then mince or grate the ginger. Thinly slice the scallions, keeping the whites and green separate. Quarter the mushrooms. Drain the water chestnuts.

Make the black bean sauce: heat 1 teaspoon oil in a medium pot over medium heat. Add the garlic, ginger, and half the Chinese five spice. Cook 1 minute, stirring frequently. Add the reserved black bean liquid and half the black beans. Add the soy sauce, chicken stock concentrate, and 1 cup water to the pot. Bring to boil, then reduce to a simmer, for 15-20 minutes, stirring occasionally.

Thinly slice the chicken breasts. Season the chicken with salt, pepper, and the remaining Chinese five-spice. Heat 1 teaspoon oil in a large pan over medium-high heat. Add the chicken to the pan and cook, tossing, for 5 minutes, until cooked through. Set aside.

Add the vinegar to the same pan over medium-high heat. Deglaze the pan by scraping up the brown bits on the bottom of the pan. Reduce liquid by half and add it to the pot with the black bean mixture.

Heat another 1 teaspoon oil in the same pan over medium-high heat. Add the mushrooms and scallion whites and cook, tossing, 5-6 minutes, until golden brown. Add the water chestnuts to the pan. Cook, tossing, for an additional 2 minutes. Season with salt and pepper.

Add the remaining black beans, black bean sauce, and chicken to the pan. Stir to combine and heat through. Taste and season with salt and pepper.

Serve divided between bowls and garnished with scallion greens. Enjoy!