Boil chicken, remove bones & skin, shred with two forks and set aside. Saute' mushrooms, onion, bell pepper, & minced jalapeno pepper until tender. Remove skillet from heat; stir in chicken and green chiles. Set aside. Combine milk powder and flour in a small saucepan. Gradually stir in water; place on medium heat-cook & stir 'til thick & bubbly. Stir in chili powder, salt, cumin, & pepper. Add to chicken mixture and set aside. Wrap tortillas in damp paper towels & then in foil & bake @ 350 for 10 min. Arrange half of the tortillas in a 12x8x2 dish;top with half of chicken mix. Repeat w/ rest of tortillas and chicken mixture. Cover and bake @350 for 25 min. Uncover and sprinkle with cheese; let stand 10 min. Top serving with tomato and yogurt. Garnish with additional jalapeno pepper slices.