Well...this is something I tried with salmon once and it actually tasted really good. Keep in mind, this was an experiment on my part, not an actual recipe.
You'll need...
1 fish (slice the meat off into a 'steak', doesn't matter if there is skin, I didn't have it. Cut the steak into strips)
1 avocado
1/2 a lemon
Seasoning of your choice (I used seasoning salt, pepper and oregano)
Turn the avocado into a paste using a fork, once pasty add lemon juice, stir till mixed.
Season to taste.
Spread it on top of fish.
Put in the oven
Cook until fish is flaky. The avocado should firm up but remain soft.
It looks ugly but it tastes fantastic.