Trim both ends off each zucchini. Slice each zucchini lengthwise into ¼-inch thick slices. Add the zucchini to a large bowl and sprinkle on the coarse kosher salt. Use your hands to toss gently so that each slice of zucchini is salted.
Let the zucchini sit at room temperature for at least 30 (but up to 60) minutes so it can release the excess liquid.
After the zucchini is done sitting, very gently squeeze each slice to help wring out the liquid and pat them dry with paper towels.
Place the zucchini slices on a paper towel-lined plate for now.
MAKE THE MEAT SAUCE:
Add the ground beef, onion, garlic, and salt to a large skillet over medium-high heat. Cook (uncovered) until the meat is browned and the onion is softened, about 10 minutes, stirring occasionally with a wooden spoon to break up the meat.
Reduce the heat to medium, add the marinara sauce, and cook (uncovered) until excess liquid has evaporated off and the sauce is thickened, about 5 minutes, stirring occasionally.
COMBINE RICOTTA MIXTURE:
Add all ingredients to a large bowl and stir to combine.
ASSEMBLE AND BAKE:
Preheat the oven to 375F. Spray the inside of a 9 by 13-inch casserole dish with olive oil cooking spray.
Spread ⅓ of the Meat Sauce in the bottom of the prepared casserole dish.
Lay zucchini slices on top of the Meat Sauce the same way you would lasagna noodles. I find that a large zucchini fits perfectly horizontally across this size dish.
Spread ½ of the Ricotta Mixture on top of the zucchini slices, and spread ⅓ of the Meat Sauce on top.
Lay zucchini slices on top of the Meat Sauce, followed by the remaining ½ of the Ricotta Mixture, followed by the remaining ⅓ of the Meat Sauce.
Spread 1 cup shredded mozzarella and ½ cup grated parmesan on top.
Bake (uncovered) until the lasagna is warm throughout and golden on top, about 40 minutes.
Once it’s done cooking, let the lasagna rest for 10 to 15 minutes before slicing and serving. Serve topped with fresh basil and more grated parmesan.
Notes
To help prevent Zucchini Lasagna from being excessively watery, don’t skip the step of salting the zucchini.
Additionally, make sure to cook the Meat Sauce until it’s thickened before making the lasagna.