Vegetable is a culinary term.
Its definition has no scientific value and is somewhat arbitrary and subjective.
All parts of herbaceous plants eaten as food by humans, whole or in part, are generally considered vegetables.
Mushrooms, though belonging to the biological kingdom, fungi, are also commonly considered vegetables.
Since "vegetable" is not a botanical term, there is no contradiction in referring to a plant part as a fruit while also being considered a vegetable.
Given this general rule of thumb, vegetables can include leaves (lettuce), stems (asparagus), roots (carrots), flowers (broccoli), bulbs (garlic), seeds (peas and beans) and of course the botanical fruits like cucumbers, squash, pumpkins, and capsicums.
Vegetables contain water soluble vitamins like vitamin B and vitamin C, fat-soluble vitamins including vitamin A and vitamin D, and also contain carbohydrates and minerals.