Slice zucchini lengthwise into thin strips, sprinkle with 1/2 tsp salt, and let drain in a colander for 10 minutes, then pat dry.
In a large oven-safe skillet, heat olive oil over medium-high heat and brown ground beef with garlic, remaining salt, and Italian seasoning, about 6-8 minutes.
Reduce heat to medium-low and stir in marinara sauce, then layer half the zucchini strips over the meat sauce.
Drop spoonfuls of ricotta cheese over the zucchini, then sprinkle with 1 cup mozzarella and half the Parmesan.
Add remaining zucchini strips, top with remaining mozzarella and Parmesan cheese.
Cover skillet and cook on stovetop for 10 minutes, then remove lid and place under broiler for 3-5 minutes until cheese is bubbly and golden.