Spread the browned and drained ground chuck evenly over the bottom of a 9x13 baking pan. Sprinkle minced onion evenly over ground meat. Layer zucchini, overlapping, over all the hamburger. Then layer potatoes overlapping, over the zucchini. NOTE: I USUALLY USE MY FOOD PROCESSOR TO SLICE THE VEGGIES, TAKES LESS TIME THEN. Place Velveeta slices over the vegetables, covering entirely, but with about 1/4" between slices. This doesn't have to be exact either.
Then repeat the entire process of layering zucchini, potatoes and Velveeta slices. There should be at least two complete layers of everything.
Heat the sour cream and the condensed mushroom soup over medium heat, stirring constantly until hot and pour this over the layers of vegetables and cheese. Using a table knife, work the creamy topping down the sides of the casserole, making sure the top is completely covered too.
Bake this for 1 hour 15 minutes, (until veggies are tender) in a 350* oven. Depending on your oven, it may take more or less time for baking. The sour cream really makes this dish wonderful.