My ridiculously easy sort-of-poached salmon:

http://boilingwater.dreamwidth.org/8289.html

A lot of fish can be cooked nicely by wrapping it in tinfoil (like a little parcel) and baking it; the tinfoil keeps it moist.

Flattish fillets of fish can be pan-fried quickly in a little olive oil or butter.

How do you feel about raw fish? If you're okay with it and have a good source of very fresh fish, it can be a lovely lazy option.

I do a summer salad with raw salmon, mango, diced onion, a bit of vinegar, and a sprinkling of coarse sea salt.