In a 5-quart Dutch oven or large heavy pot, heat 1 tablespoon oil over medium-high. Season chicken with salt and pepper. Add half of chicken to pot and cook until browned on all sides, 6 to 8 minutes; transfer to a plate. Repeat with remaining oil and chicken.
Add onion and garlic to pot (reduce heat if browning too quickly) and cook, stirring, until softened, 4 to 6 minutes. Add wine and chicken (along with any accumulated juices) to pot and bring to a boil. Cover pot; reduce heat to medium and cook 5 minutes.
Place greens on top of chicken; season with salt and pepper. Cover and cook until chicken is opaque throughout and greens are wilted, 3 to 5 minutes more. Remove from heat and stir in lemon juice and olives. Serve greens and chicken drizzled with pan juices with lemon wedges on the side.