Eggplant parmesan. Eggplant, sauce (organic if you want. Paul Newman marinara is quite nice), and cheese. Let the sickly bastard eat something calorie dense for once.
Wait... vegan means no cheese, right?
That's the only main-dishy thing I can think of.
You can sautee squash and zucchini with some herbs, but that's more of a side dish.
I'm assuming potatoes are out as well?
Hell, just serve raw veg with a simple vinaigrette.
Oh... wait! That's it. Grilled portobello mushrooms. Hell, grill the zucchini and eggplant as well. You should serve it with a multi-vitamin garnish since diet-princess over there surely needs it.