Step 1

Brown Beef: Add ground beef to high-sided pan (Note over medium-high heat. Crumbling beef with stiff utensil, cook until browned and released water has evaporated, 7 to 8 minutes. Optionally, drain off grease in pan, especially if using less than 90% lean beef.

Step 2

Make Tomato Sauce: Add onions to pan with ground beef over medium-high heat. Cook until onions are softened and translucent, stirring occasionally, a few minutes. Reduce to medium heat, and stir in tomato sauce. Simmer until sauce is thick and clings to meat and onions (important for liquid control; Note 9), stirring frequently, about 10 minutes. Stir in oregano, salt, and cayenne until well-mixed, about 1 minute. Turn off heat.

Step 3

Prep Oven & Cut Zucchini: Position oven rack in lower half of oven, and preheat to 375 F. For each zucchini, slice off and discard both ends. Stand zucchini vertically on a stable flat end, and carefully slice into 1/8 to 1/4 inch thick strips along the length (Note 10).

Step 4

Assemble Lasagna: Arrange one-third of zucchini slices along bottom of 8x8 inch baking dish, slightly overlapping each other. Evenly spread half of meat sauce over zucchini slices. Distribute 1/2 cup of mozzarella over meat sauce. Repeat with another zucchini layer, meat sauce layer, and mozzarella layer. Top with remaining zucchini slices. Add another 1/2 cup mozzarella and 1/2 cup parmesan over zucchini slices. Give baking dish a quick shake so that cheeses spread out and settle into cracks. (See Note 11 for make-ahead option.)

Step 5

Bake & Serve: Bake uncovered at 375 F until lasagna is golden brown on top, about 45 minutes (Note 12). Cool for 15 minutes to allow lasagna to set and cease bubbling before slicing. Serve (Note and store any leftovers (Note 14).