Heat a high-sided pan over medium heat until hot (I use a 10-inch wide nonstick pan with 3-inch high sides). Add olive oil to coat the bottom of the pan. Add onions and cook until softened, about 5 minutes, stirring occasionally.
Add ground beef to the pan. Cook until it's no longer pink, about 5 minutes, breaking it apart as it cooks.
Add tomato sauce, stirring it in. Bring to a simmer over medium-high heat, then gradually reduce the heat as needed to maintain a simmer. Simmer for about 10 minutes to thicken the sauce, stirring frequently. The resulting sauce should be thick, easily clinging to the meat and onions; this helps reduce excess moisture in the resulting lasagna.
Add oregano, salt, and cayenne. Stir for a minute until well-mixed. Turn off the heat.
Assembling and baking the lasagna:
Position an oven rack in the lower half of the oven, and preheat to 375 F. Set aside an 8x8 inch baking dish.
For each zucchini, slice off both ends and discard them. Stand the zucchini vertically on a stable flat end, and carefully slice along its length into 1/8 - 1/4 inch thick strips. Don't worry if the slices aren't perfect because it won't affect the deliciousness of the lasagna.
Arrange about one-third of the zucchini slices along the bottom of the baking dish so that they are slightly overlapping in a criss-cross pattern. Evenly spread about half of the meat sauce over the zucchini. Distribute about 1/2 cup of mozzarella cheese on top of the meat sauce.
Repeat with another zucchini layer, a meat sauce layer, and a cheese layer.
Top with remaining zucchini slices. Add another 1/2 cup mozzarella cheese and 1/2 cup parmesan cheese on top of the zucchini. Give the baking dish a quick shake so the cheeses spread out and settle into cracks.
Bake uncovered at 375 F until the lasagna is golden brown on top, about 45 minutes. Let it cool for at least 15 minutes to allow the lasagna to set and cease bubbling before slicing.
Makes 4 Servings
Amount Per Serving (quarter of 8x8 casserole):
Total Fat 23g
Saturated Fat 11g
Net Carb 8g
Total Carb 12g
Dietary Fiber 4g
Vitamin A 21% · Vitamin C 41% · Calcium 41% · Iron 23%
Recipe from Savory Tooth at https://www.savorytooth.com/zucchini-lasagna/