Slice the zucchini into ½" rounds. Put the rounds in a sieve or colander over the sink or a bowl and sprinkle with salt, tossing to coat.

Allow the salted zucchini to sit for 15 minutes to draw out excess moisture.

Rinse well under cold water to remove the excess salt. Pat dry with paper towel.

Heat the oil in a large skillet over medium high. Add onions and cook until they begin to soften, about 2 minutes.

Add garlic and ground beef, breaking up with a spoon, and cook, stirring often, until the meat is browned with no trace of pink, about 5 minutes.

Stir in the tomatoes, Italian seasoning, salt and pepper. Remove from heat.

Preheat oven to 350°.

In an 8x8 baking dish, spread half of the ground beef mixture. Cover with half of the zucchini slices, then half of the mozzarella cheese.

Repeat the above steps with the remainder of the meat mixture, zucchini slices, and cheese.

Bake in the prepared oven for 20 to 25 minutes, until the cheese is melted and beginning to brown.

Allow the casserole to rest for 10 minutes before serving.