Sprinkle cleaned chicken pieces with salt and pepper. In a heavy skillet, heat oil on medium high heat. Brown chicken on all sides. Push to side of skillet, add the onions, garlic and mushrooms. Cook and stir for a few minutes. In a small bowl, mix the tomato paste with other ingredients. Pour over chicken, stirring well. Cover and simmer very gently until chicken is tender. (about 30 minutes). Uncover and simmer until sauce is to the thickness of your liking.