Heat oven to 350°F. Cook pasta according to package directions; drain well. In large bowl, whisk together remaining pasta shell ingredients. Add pasta; toss to coat. Arrange pasta in 9 inch pie dish, pressing down and up side to form shell; set aside.
Meanwhile, heat large nonstick skillet over medium heat until hot. Add ground beef; brown 4 to 5 minutes until beef is 160°F on a meat thermometer, breaking up into ¾ -inch crumbles. Pour off drippings. Season beef with 1 teaspoon garlic powder, ½ teaspoon salt and cumin; stir in tomatoes. Bring to a boil; cook 3 to 5 minutes until liquid is almost evaporated, stirring occasionally.
Reserve 2 tablespoons beef mixture for garnish. Stir sour cream into remaining beef; spoon into pasta shell. Place 1 cup cheese in center leaving 2-inch border around edge. Spoon reserved beef mixture onto center of cheese; bake in 350°F oven 15 minutes or until heated through.