Combine first 6 ingredients in a bowl; stir with a whisk. Set aside.
Place the breadcrumbs in a shallow dish. Dredge the chicken in the breadcrumbs. Heat the olive oil in a large nonstick skillet over medium-high heat. Add the chicken, and sauté 3 minutes on each side or until chicken is golden brown. Remove the chicken from pan, and keep warm. Add leek and mushrooms to pan, and sauté 2 minutes or until mushrooms are lightly browned. Return chicken to pan, and stir in broth mixture. Cover the mixture, and simmer 10 minutes or until the chicken is done.