To add to the quesadillas - I really like "squashadillas" - Same idea, just with squash in the middle. Yummy!
Do you have a lot of different spices in the house? If so, you can make up a big pot of what I shall call "the basic vegan dinner base." Get some chickpeas (or other bean/legume), some assorted vegetables, and a grain. Have this all in a pot. Scoop some out, and just toss or stir-fry or sautee or whatever it with whatever spice you're feeling for the night. So with the same batch of ingredients, you can have chana masala one night, sweet and sour the next, spicy mexican, etc etc.
Ways to have fruit:
In casserole - such as an apple-raisin kugel (which I have an awesome recipe for if you want, PM me)
In sauces - such as pineapple in sweet and sour sauce
In salad - mandarin oranges on an asian inspired salad, or a mango slaw w/ shredded lettuces and cabbage, carrots
In terms of making casseroles for one - it can be done. Just get a smaller dish.
Like one of those mini loaf pans. A mexican casserole of this nature is very easy - layer tortillas, beans, salsa, fake cheese, guac... Just only use one can of beans, and half the pack of tortillas, ya know?
How about soup and sandwich? Very easy dinner for one.
You can't make one "slice" of pizza, but you can make one pizza bagel. Or one pizza english muffin. Or one french bread pizza.