Preheat oven to 500ºF. Coat a baking sheet with cooking spray and spread tomatoes and zucchini over sheet. Roast vegetables for 10 to 12 minutes.
Meanhwile, in a large, nonstick skillet, saute beef, onion and garlic until beef is browned. Stir in tomato sauce and bring to a simmer.
Spread beef mixture in a large, shallow baking dish (3 quart or 9 X 13-inches) and top with roasted vegetables. Reduce oven temperature to 350ºF.
Whisk together cottage cheese, egg yolk, cheddar cheese, herbs, salt and pepper in a medium bowl. Spoon over roasted vegetables and smooth with a rubber spatula.
Bake until very hot and bubbling around edges, about 35 minutes. Cut into six equal pieces and serve immediately. (Note: If preparing casserole in advance and freezing it, make sure to thaw it completely in the refrigerator before baking it. Increase the baking time by 5 to 10 minutes.)