Preheat oven to 375 degrees F (190 degrees C). Lightly grease a 9x13 inch baking dish.
In a large skillet over medium heat, brown the ground beef. Drain the beef, and mix in the zucchini, onion, garlic, and marjoram. Cook and stir until vegetables are tender. Mix in the salsa, tomato soup, and corn. Season with 1 teaspoon salt. Transfer to the prepared baking dish.
In a medium bowl, mix the flour, baking powder, sugar, cream of tartar, 1/2 teaspoon salt, and garlic powder. Cut in the butter until the mixture resembles coarse crumbs. Stir in the Cheddar cheese, sour cream, and milk. Spread over the beef mixture in the baking dish.
Bake covered in the preheated oven 25 minutes, or until the topping is golden brown and a toothpick inserted in the center comes out clean.
