Sometimes you are tired yet hungry and end up just eating a sandwich for dinner. This is not such a terrible thing. It's not like you're having a bag of doritos for dinner, for example. You are having real food. If you take a couple minutes to actually cook said sandwich, it turns out even better.

This kind of thing works really well with nearly anything you have in the vegetable drawer. I mean, I probably wouldn't use potatoes, but other than that, close to anything goes.

decent bread, in this case half a baguette
olive oil
yellow onion
grape/other tomatoes
mild white cheese
salt, pepper, parsley

Slice some bread or split a baguette precariously down the middle. Anoint it with oil. That's right: indoctrinate your bread.

Sliver some onion and tomato into the thinnest slices possible. You can use whatever kind of onion/shallot/etc and tomato you have lying around, although I wouldn't recommend midwinter tomatoes or anything. Layer the slices onto the bread. Add some salt and pepper and stick the business into the oven. I had a bunch of fries already baking at 350F, so I just stuck my sandwich on the other rack.

After 5 or 10 minutes, check on your progress. If the onions have softened and the tomatoes have begun to crumple, it's time for cheese. You can clearly do this without cheese as well, although the finished product will lack a certain gooey quality. Slice some cheese thinly and layer it over the vegetables. You don't need too overabundant an amount. I used mozzarella, but whatever you have lying around should be fine.

Stick everything back in the oven for another five minutes, or until the cheese starts to turn toasty brown on top. Then whip out the pan, add some parsley/any other fresh greens you might want, smash your sandwich closed, and eat.