What is easy to cook, healthy, cheap AND easily available?

I am currently working on changing my diet and improving my general health. This has involved eating smaller portions, eating less (basically no) junk food, and getting back in the habit of exercising regularly.

The problem is, I really like to cook. And… Unfortunately, most of the things I like to cook tend to be a little on the unhealthy side. Heck, I don’t even know how to cook things that are healthy that don’t just come out of a box or bag and get microwaved or baked.

I have no idea where to begin, when it comes to preparing a healthy dinner. I like meals that aren’t just.. Out of the box. They are boring. Any suggestions will be loved, thoroughly.