For my veggie lasagna, I use the new Ragu Homestyle Spaghetti Sauce in any flavor except the Meat Sauce. None of the other varieties list meat as an ingredient. I am very picky about my spaghetti sauce, and swore off anything from a jar or can for most of my life, but the Ragu Homestyle is almost as good as the sauce I cook from scratch.
I mix ricotta, parmesan, romano, and mozzarella cheeses with an egg or two as a binder.
For the pasta, I use the kind that does not need to be boiled. I thinly sliced onions, carrots, tomatoes, mushrooms, squash, eggplant--pretty much any veggie I have on hand.
I do not usually add the extra liquid the no-boil lasagna noodles call for, as the vegetables usually release more than enough liquid to re-hydrate the noodles. Often, instead of pasta, I will thinly slice eggplant and/or zucchini lengthwise, and use that in it's place for a low carb option.
I layer sauce, pasta, cheese mixture, and veggies. If I'm using a deep dish, I will repeat the layers, and top with a final layer of pasta (or eggplant/zucchinni) and sauce. If it is a shallow dish, I just add the top layer of pasta and sauce.
I cover and bake at 350 for 35 minutes for a shallow dish, 1 hour for a deep dish. Then I uncover it, sprinkle with mozzarella and cook an additional 5-10 minutes until the cheese is melted and starting to brown a bit.