If it's not too late, I tend to make part of the meal the day before. So I'd suggest you do some sort of bake in a white/cheese sauce - just something to make the day before that looks impressive that you just put into the oven on the day.

Here are a couple of easy ideas:
Brocolli and Salmon bake
You need: brocolli (100g/person), salmon (1 fillet/person), potato wedges (2-3 potatoes/person or oven wedges, 100g/person), cook them all then add them to a pie dish, top with a cheese sauce with some parsley in, needs to oven bake for 30mins on the day.

Fish Pie
Fresh fish, carrots, peas, sweetcorn, mash potato, white sauce.
Add the uncooked fish to a casserole dish, then add the cooked carrots, peas and sweetcorn. Cover with a white sauce of medium thickness. Put the mash potato on the top - again, needs 30-40 mins in the oven on the day.