Well, my go-to fancy dish is salmon. Get a big fillet.
Make a glaze of equal parts prepared mustard and olive oil. I like to combine a couple of different kinds of mustard. Colmans prepared mustard is smooth and spicy. A dijon mustard is a nice substitute for that. To the Colmans, I add something a little grainier; my current fave is a mass market plastic barrel with a Polish-esque name. If you're really thinking ahead, finding or making a tarragon mustard would be ideal.
I'm never that organized.
Pair the quarter cup of the mustard with a similar quantity of olive oil. The recipe that I work from says to add 6 cloves of chopped garlic, a quarter teaspoon of ground red pepper, the juice of one lemon and a teaspoon of capers, along with salt to taste.
I say "the recipe that I work from" because while I almost always use all of these ingredients, I would swear that I never use the same amounts twice.
Coat the fish with the mixture (I usually just do the flesh side of the fillet), let it sit for a bit and then bake it at 375 degrees F for about 45 minutes. It's also grillable.
* although she's invited, it's unfair to always rely on Tona to go play in the sink after dinner...