Sorry if it's too late for tonight's dinner, but here it is:
Chop or dice (usually, the more you chop things up, the better they all mix together in the soup)
1 medium-large onion
1 or two celery stalks - if you have the leaves, chop a handful of those up, too.
1 big fat carrot
Depending on your tolerance for such things, you might also want to include a parsnip or swede, but be aware that these will add distinctive flavour to your soup.
Heat up either a tablespoon of olive oil, or a tablespoon of canola oil, or half-and-half butter and one of the preceding oils.
Toss the onion and the celery into the oil, and cook at a medium heat for five minutes or so.
Add the carrot and the potato; make sure they're both well coated with the oil. Add more oil or a little water if things are getting hot and dry.
Add: One large can of diced tomatoes (with juice), one can of navy or other small beans drained, one L. Tetra pack of your choice of Chicken stock or Vegetable stock - it depends on how Veggie you're being here. If you want it to be more tomato-y you can add a tablespoon of tomato paste. I might also add some chopped parsley at this point.
Simmer all this for 1/2 an hour or until the potatoes and carrots are done to your taste.
You can also throw in a can of niblets corn should you feel so inclined.
If you want something more Italian, add some Italian seasoning, or oregano and basil. But with sufficient onion and celery you should have a good wholesome tasty veggie soup without any further seasoning (you might want to add salt and pepper to taste)