Cook ground beef in a large nonstick skillet, stirring until beef crumbles and is no longer pink; drain.
Cook zucchini, onion, and garlic in skillet, stirring occasionally, 6 to 7 minutes or until vegetables are tender. Add ground beef; stir in pasta sauce and 2 1/2 teaspoons Greek seasoning. Cook over low heat 3 to 5 minutes or until thoroughly heated. Pour beef mixture into a lightly greased 3-quart round baking dish.
Prepare frozen mashed potatoes according to package directions. Stir together mashed potatoes, remaining 1/2 teaspoon Greek seasoning, crumbled feta cheese, lemon rind, and lemon juice. Spoon potato mixture evenly over beef mixture; smooth with back of spoon to cover beef mixture completely.
Bake at 400° for 25 minutes or until potatoes are lightly browned.
Note: For testing purposes only, we used Emeril's Roasted Red Pepper pasta sauce.