Preheat oven to 425F. Toss zucchini and eggplant with olive oil, and salt. Arrange on two baking sheets, roast in the top and bottom thirds of the oven for 10 minutes switching sheets halfway through. Let cool until safe to handle.
Spread 1/4 cup marinara sauce on the bottom of an 8x8" baking dish. Top with 4 slices of eggplant, followed by 1/4 cup of marinara sauce, dot with ricotta cheese, layer 4 zucchini slices crosswise on top of eggplant, top with 1/4 cup marinara sauce and dot with ricotta cheese. Repeat with remaining layers, finishing with zucchini, 1/4 cup marinara sauce and 1/3 cup grated mozzarella cheese.
Roast in the oven for 20 minutes or until cheese is melted and bubbly.
Allow to cool for 10 minutes, sprinkle with fresh basil and cut into 6 slices.