HEAT oven to 400ºF. Prepare Kraft Dinner as directed on package, omitting the butter. Meanwhile, brown meat in large nonstick skillet; drain. Stir in tomatoes and oregano; cook until heated through, stirring occasionally.

COMBINE Kraft Dinner and meat mixture; spoon into 9-inch square baking dish. Top with Cheddar.

BAKE 10 min. or until Cheddar is melted and casserole is heated through.