I had the fennel orange salad when I made lasagne recently, and it cut the richness perfectly.
My other choice would have been arugula salad with a light lemon or orange and olive oil dressing, but given the greens in your lasagne, the fennel would be more different than arugula.
Another idea is a beet salad – I did that one with oranges recently too. A bit sweet and a bit tart to balance the richness. I did batons for the beets, but you could thin-slice them for prettier plating.
Agree with @MunchkinRedux about skipping the garlic bread, especially as it’s a white lasagne.
If you think some people will miss meat, how about sausage-stuffed mushrooms as a side?
Or you could have charcuterie beforehand. (I’m not a big fan of chopped meat in antipasto form, but some prosciutto crudo or mortadella is always a welcome bite.)
