I am so excited for you! We haven't been on the Navigator but were on the Voyager (sister ship) and it was beautiful - an amazing cruise. Here are my recommendations:
Garlic soup - if you like garlic it's delicious
Scallop risotto - even if you don't like scallops it's worth it
Choco chino trilogy - for the chocoholic!
Chocolate raspberry ganache tart (I think this one is on the lunch menu)
Steak sandwich (also lunch menu, but it's an entire steak on a sandwich)
Tiramisu - at the Cafe Promenade which has lots of other chocolate treats too
We have pictures from the Voyager on our gallery: