Preheat the oven to 425°F. Line 2 baking sheets with parchment paper.
In a large bowl, toss the sliced zucchini with olive oil, Italian seasoning, salt, and pepper.
Lay the strips of seasoned zucchini in a single layer on the baking sheets.
Bake for 15-20 minutes, until the zucchini is soft and fork tender.
Reduce the oven to 375°F.
Layer the casserole: in a 7×10 casserole dish, add a thin layer of marinara sauce.
Lay a single layer of baked zucchini strips.
Add another thin layer of sauce, followed by a layer with a third of the mozzarella cheese, parmesan cheese, and basil.
Repeat layering twice in this order for a total of three layers. The final layer should be mozzarella and parmesan cheeses with some basil.
Bake in the oven for 25-30 minutes, until the edges are bubbling and the cheese on top is completely melted and lightly browned.
Let the casserole sit for 10 minutes before you slice it into 6 squares for serving.
