One of my favorite greens is Swiss Chard. It grows abundantly, it's a biennial, so if you mulch it nicely in the fall, you will have really early greens the following spring. Just be sure, during the second year, to clip the seed stalk which the plant wants to send up early, as soon as it appears. It can get 2 ft tall practically overnight (it seems like anyway) and when that happen, the tasty leaves die back and all th energy goes into producing a huge amount of seeds.
Swiss Chard leaves have a thick rib that runs lengthwise down the middle of the leaf. This is edible and quite tasty, but some people don't like it. It does add to the cooking time. If you are in a hurry. . . simply fold the leaf in half lengthwise along the rib, and use a sharp knife to cut it out. Then saute or braise the leaves and lunch is ready. Since I don't like to let anything go to waste, I would then refrigerate the chard ribs and use them in something else that takes more cooking.
Cooked Swiss chard, like other cooked greens, freezes well.
Great companion flavors include all the aromatics (onions, garlic), hot peppers, celery, cheese, milk, cream, yogurt, cumin.
Speaking of celery. . . I am growing celery this year for the first time. It seems very slow growing. I started the plants early in March and they are all of 2 inches tall. I just transplanted them into containers (I am doing a lot of container gardening this year) and they took the transplanting fine. They may be only 2 inches tall on top, but the roots were very developed and extensive. Even though I had just broadcast the seeds on the flats, it wasn't a hassle to untangle them. I used a knife to cut out a clump, and then I gently shook them until the potting soil fell off and the plants naturally separated.
So now I have 32 celery plants in various pots (1 to 4 plants/pot depending on the size).
I'm growing my chard this year in pots, I want to bring some of them inside to overwinter and maybe with a grow light or two see if I can tease some leaves out during the cold of our Oklahoma winters.