A meatless lasagna is always filling. Tastes great with any chopped greens in the spinach family: mustard, kale, Swiss chard, or even a combination. Or a mushroom lasagna (great TNT recipe by Rose Shulman @ the NYT’s Cooking section) which works for vegetarian, vegans, and even carnivores.
Other possibilities? A cottage pie which is pretty much the same as a shepard’s pie minus the meat and with lots of mushrooms. I like to use a mix of Portobellos with a little dried porcini added but any kind will do. A bean and vegetable stew is a choice that would take up no valuable oven space. Most the above dishes can be put together fast, ,have about an hour cooking time and can be prepared in advance and then reheated when needed.