Lay zucchini slices on paper towels and sprinkle both sides with kosher salt. Let sit 15 minutes to release moisture, then blot firmly with more towels. This step prevents watery lasagna.

Preheat oven to 425 degrees F. Arrange slices on two parchment-lined baking sheets, brush lightly with olive oil, and roast 12-15 minutes until just tender and slightly dry. Set aside to cool. Reduce oven to 375 degrees F.

Heat a large skillet over medium-high heat. Add beef and sausage, breaking up with a wooden spoon. Cook 6-8 minutes until well-browned and cooked through. Drain excess fat if needed.

Add garlic, oregano, and red pepper flakes to the meat. Cook 1 minute until fragrant. Stir in marinara sauce, reduce heat to low, and simmer 10 minutes to thicken slightly. Taste and season with salt if needed.

In a bowl, combine ricotta, 1 cup mozzarella, parmesan, beaten egg, and chopped basil. Stir until well blended.

Spread 1 cup meat sauce in the bottom of a 9x13 inch baking dish. Add a layer of zucchini noodles (slightly overlapping), half the ricotta mixture, and 1 cup meat sauce. Repeat layers once more, ending with a final layer of zucchini. Top with remaining 1 cup mozzarella and extra parmesan if desired.

Cover tightly with foil and bake 30 minutes. Remove foil and bake 15-20 minutes more until bubbling and cheese is spotty golden. Let rest 10 minutes before slicing - this sets the layers so they hold together.

Garnish with fresh basil leaves and extra parmesan. Cut into squares and serve warm.