Often, nutrition gurus will say you should eat your vegetables raw. True, some vegetables are best eaten raw in terms of nutrient content, but many benefit from cooking in order to make the nutrients easier to absorb. The best cooking option is steaming.
Carrots are one exception to the raw is best theory. The beta carotene absorbed in the gut from cooked carrots can be five times higher than from raw. Steam them to keep from over-cooking and mash them if you like. Broccoli and spinach also offer high levels of beta-carotene when cooked.
Lycopene, found in tomatoes, can help prevent cancer and degenerative eye disease, but the benefits are only realized if the tomatoes are processed or cooked. To steam a tomato, slice an "x" into the base, place in gently boiling water, and let sit for a few minutes. Cool them off in cold water and peel them to add to any dish. Try them on toast.
Lutein is found in spinach, kale, and other yellow vegetables, but is more easily taken up by the body when the vegetables are cooked. Otherwise, the lutein stays locked within the cellular walls of the plant. Even happier news is that lutein works best with a source of fat, like butter or olive oil. Lutein may help prevent macular degeneration, so if you value your sight, steam some spinach and give it a pat of butter.
Keep in mind that you gain the most from eating vegetables by eating a lot of them. However you prefer to prepare and eat carrots, spinach, broccoli, tomatoes, beans, radishes, or Brussels sprouts, you should do so often. Your body gets essential nutrients from this important food source and absorbs them better from vegetables than from supplements. If a bit of butter helps them go down, go for it.