One nice easy preparation is "poisson en papillote"; fish and veg wrapped in parchment paper (or you can use foil, but parchment makes a nicer presentation.
Basically I mound veg and fish on a sheet of parchment (about 15" square paper), then lay another sheet of parchment on top, and fold/roll/crimp the edges working around the perimiter until you have a tight seal; bake in 400F over for about 20 minutes until fish is done. There is a good pictoral here..cookingfortwo.about.com/od/maindishes/ss/enpapillote.htm
If you are using a relatively thin or delicate fish that will cook quickly, then I like to drop my veg in boiling, salted water for a few minutes to blanch, then drain and use; but if you are using a thick salmon or thick halibut, etc. fillet then the veg will probably cook in about same time as fish.
If you want a starch to be included, a nice easy addition is to slice a small yam into 1/8" thick medallions and layer them on the paper, then mound the veg over top, and season w/ salt/pepper. A few leafs of basil is nice or your favorite herb (sprig of thyme is good also), and a small bit of butter (1t). Season fish (old bay is nice, or any of your favorite cajun or other spice rubs, or whatever you like, and salt), lay fish on top and another couple bits of butter.
Some liquid in the pouch is nice like white wine, or stock, or sherry, but not too much (4T is usually lots), as you don't want to "boil" the ingredients, but instead you want the moisture to steam everything.
I put each parchment pouch on its own baking sheet, cut a 1" slice in the top of each to let some steam/moisture escape, and after 20 mins at 400 you can poke a knife through this opening to feel for doneness of your fish and veg. Slide onto a plate and let yourself and guests open - real nice with some fresh bread to sop up the liquid, and a glass of white. Mmmm.
One other thing I like about this cooking method is if you are having fish on a cool summer day outside, it can get cold quickly, but if you serve "en papillote", you can open outside and the little pouch keeps everthing warm while you eat. very nice. enjoy!