Preheat oven to 350 degrees F. Cook pasta according to package directions; drain. Rinse with cold water; drain again.
Meanwhile, divide about 1 cup of the salsa between two ungreased 2-quart rectangular baking dishes, spreading evenly. Set aside. In an extra-large skillet cook ground meat over medium heat until brown. Drain off fat. Stir in cream cheese and chili powder. Cool slightly.
Spoon meat mixture into cooked pasta shells. Arrange filled shells on top of salsa in dishes. Top with the remaining salsa.
Bake, covered, for 15 minutes. Sprinkle with cheddar cheese. Bake, uncovered, about 15 minutes more or until heated through. If desired, sprinkle with tomato.