To a large pan over medium heat, add oil, chicken thighs and onions until they begin to brown -- about 5 min. Add remaining veggies, turmeric and salt. Combine. Add a little water if necessary, cover and cook until chicken is done -- about 15 minutes. Add yogurt and garam masala and mix to combine. Reduce heat to low and simmer until sauce thickens slightly. Serve with Indian bread (Naan) or a warm pita.