Pre-heat the grill. I used my gas grill outside, but you could also use a grill pan on the stove. I have an All-Clad LTD Grille Pan and I use it all the time, especially when I want to grill something small and quick. But for a batch of vegetables this size, grilling outside was faster, easier, and cooler!
Cut off the ends of the zucchini and slice lengthwise, about 3/8" thick. Cut off the end of the eggplant and slice lengthwise, about 3/8" thick.
Drizzle the vegetables with olive oil and grill until tender.
Preheat the oven to 350 degrees.
To assemble the dish, put a couple of tablespoons of marinara sauce on the bottom of a 9"x13" baking dish and spread around to cover the bottom of the pan.
Put down a layer of grilled zucchini slices. On top, add some crumbled ricotta (about 4 oz), parmesan cheese (2 oz), mozzarella cheese (2 oz), and dot on top more tomato sauce. Sprinkle on some of the chopped mixed herbs.
Repeat the process with a layer of grilled eggplant. For the top, I had just enough of zucchini and eggplant to alternate to make a 3rd layer. Top with remaining sauce, cheese, and herbs.
Cover the pan with foil and bake for 30 minutes. Remove the foil after 30 min and let the top brown, about 5-10 minutes more. Remove from the oven and let rest 5-10 minutes; it's easier to cut when it cools slightly.