In the Greek version of baked ziti, the noodles are mixed with two sauces: a lamb-and-tomato sauce and a milk-and-cheese sauce. I lightened the cream sauce by using 2% milk and fewer eggs. The casserole keeps for days in the refrigerator and cuts into neat little squares for reheating.
Heat a large skillet over medium heat. Add oil to pan; swirl to coat. Add onion; sauté 5 minutes or until tender. Add garlic; sauté 1 minute. Add lamb and beef; cook 4 minutes or until browned, stirring to crumble. Add tomatoes, oregano, 1/2 teaspoon salt, and cinnamon; bring to a simmer over medium-high heat. Reduce heat to low, and cook 20 minutes, stirring occasionally and mashing with a spatula or flat side of a wooden spoon. Remove from heat; set aside.
While sauce cooks, melt butter in medium saucepan over medium heat. Add flour, stirring with a whisk. Cook 1 minute, stirring constantly. Add 1/2 cup milk, stirring with a whisk until smooth. Gradually add remaining 2 1/2 cups milk and remaining 1/2 teaspoon salt, stirring until smooth. Bring to boil over medium-high heat, and cook 1 minute or until slightly thick. Remove from heat. Gradually add hot milk to eggs, stirring constantly with a whisk. Stir in 1/2 cup cheese. Keep warm.
Preheat oven to 350°.
Cook pasta in boiling water 9 minutes or until al dente, omitting salt and fat. Drain. Stir 3 cups pasta into tomato sauce; stir remaining 3 cups pasta into white sauce.
Spoon tomato-sauced pasta into a 13 x 9-inch glass or ceramic baking dish coated with cooking spray. Top with white-sauced pasta, spreading evenly. Sprinkle with remaining 1/4 cup cheese and breadcrumbs. Bake at 350° for 30 minutes or until bubbly. Let stand 5 minutes; sprinkle with oregano leaves, if desired.