The mussels are a nice starter. I also like the octopus. Sometimes we'll split the special pizza of the day. For mains, I like to hear what the specials of the day are. Fish of any kind is always a good order and the pasta specials are very reliable. My fallback dish is pappardelle with braised rabbit. Dessert is either the crostata of the day or a few scoops of gelato that come from Il Laboratorio del Gelato.
I haven't been to Lavagna in a while, either, but with that caveat, I've found the following to be knockouts:
Carciofi al forno (wood-oven roasted artichoke hearts with white bean puree and cremini)
Rigatoni with sweet fennel, spicy sausage, peas, and cream
Whole wood-oven roasted fish for two, flambeed, with sauteed spinach and grape tomato relish
I think I remember liking the monkfish, too. In fact, I think I've tried all the secondi and liked them all. The appetizer and pasta I listed are really superior to all the other choices, though, I believe.