1Heat oven to 350ºF. Grease or spray 11x7-inch (2-quart) glass baking dish. In 10-inch skillet, cook beef, 1 teaspoon salt, the pepper and garlic over medium heat, stirring occasionally, until beef is brown; drain.
2In 3-quart saucepan, heat water, butter, 1 teaspoon salt, the onion and oregano to boiling. Remove from heat. Stir in milk and dry potatoes just until moistened. Let stand about 30 seconds or until liquid is absorbed; whip with fork until fluffy. Spread half of the potato mixture in baking dish. Layer with beef and half of the tomatoes. Top with remaining potatoes and tomatoes; sprinkle with cheese.
3Bake uncovered about 30 minutes or until hot and bubbly.