How to Make It
Heat oil in a large skillet over medium-high. Sprinkle chicken with salt and pepper. Cook, turning occasionally, until evenly browned, 6 to 8 minutes. Remove from skillet.
Add onion to skillet; cook, stirring often, until tender, about 5 minutes. Add greens, tomatoes, beans, and stock. Bring to a boil; stir in red wine vinegar and sugar. Return chicken to pan, cover, and reduce heat to medium. Simmer until thermometer inserted in thickest portion of chicken registers 160°F and greens are just tender, about 10 minutes. Serve with pepper vinegar.