Heat 1 tablespoon oil in a 12-inch skillet over medium-high heat. Add the chicken and cook until well browned, stirring often. Remove the chicken from the skillet. Heat the remaining oil in the skillet over medium heat. Add the mushrooms and cook until tender, stirring occasionally. Add the garlic, tomatoes and onions to the skillet and cook and stir for 1 minute. Return the chicken to the skillet. Stir in the concentrated broth and water and cook until the chicken is cooked through.