HEAT oven to 400ºF. Prepare Dinner as directed on package, omitting the butter. Meanwhile, brown meat in large nonstick skillet on medium-high heat; drain. Add tomatoes and oregano; mix well. Bring to boil.

ADD meat mixture to Dinner; spoon into 9-inch square baking dish. Sprinkle with Cheddar.

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