Can you train yourself to like certain foods?

Try to eat things that you don't know the contents of, unless you have allergies. For example, I hate mushrooms but have found that I loved mushrooms on pizza provided that I don't know they're there. If I do then I go out of my way to pick around them. If you have someone who can cook for you, like a parent, then request that they try to add vegetables to their recipes. Cauliflower makes an excellent substitute for parmesan cheese on things like spaghetti if you aren't cognisant of it's presence.

Load up on leafy greens when making a sandwich (try to eat more sandwiches, too. Good for you.) Making a bologna sandwich? Toss on some lettuce. Also, brown bread and rice is better for you than white. So if you're not already on that, make the switch.