There is no botanical definition for a ‘vegetable’, it’s more what they’re used for than how they grow. Most of what we eat as vegetables are fruits (like a tomato), leaves (like lettuce), flower buds (like broccoli), stalks (like celery) or a type of root (like ginger or potato).
Tomatoes are legally defined as vegetables in the USA, but that’s because of an 1893 Supreme Court ruling involving the taxation of imported vegetables.
Well, after it’s been boiled to death, not much else you can do with it. Lightly steamed, to the point where it is softening but still has a little firmness to it, is the way to go. My wife likes hers with lemon, I don’t even salt it.