Oily fish are a great source of omega-3 as well as heme iron. Salmon was one of our "staples" for DS's meal times at that age. I tried to have it at least twice per week. One of the other reasons, aside from the nutritional aspect, that I liked with salmon was that is was sooooo easy to prepare!
We would buy a large fillet, skinned and boned and then cut it up into chunks about 2" x 2". Wrap individually in cling film and then foil and pop them all in the freezer. On salmon days they took only a few minutes to defrost in a bowl of water, so it meant that if I had forgotten to take something out for LO's dinner salmon would always be ready in a pinch. Once fish is defrosted, then a few inches of milk (we used formula) in a saucepan and bring to a simmer. Put fish in, simmer for 4-5 minutes until the salmon is flaky. That's it - done! It's nice with white sauce or cheese sauce over it (my LO was milk allergic so I couldn't). I used to flake the salmon and mix it with some pureed apple or pear, or mush it with avocado. He also liked it with a mix of carrot, cauliflower and tomato mushed together.
Now he's taken a dislike to it cooked that way, we still try to do salmon, tuna, mackerel, or sardines twice per week. If it is salmon or tuna, I mix it together with cream cheese and use it as a sandwich spread. Mmmmm.