It's certainly not necessary but will add a bit of a tangy zip that might appeal to you. Does the lemon get mixed with the ricotta and spinach? I would just give it a taste first and see what you think without the lemon. Could be the tomato paste and tomatoes in the sauce are enough for your taste. Half of a medium lemon can give you roughly 1/2 tablespoon of zest, give or take. If your taste buds think it needs the lemon, start with less, but, yes, very easy to omit.

Agreed. It's quite normal to add lemon zest to ricotta (or to spinach) for a baked dish like this (I do), but you don't need it. Some use a little nutmeg, as if it were bechamel. Plain should be fine. I like it and wouldn't omit it, but if it doesn't appeal to you the dish won't be bad without it.

^Good suggestion for the nutmeg if you like it. I add it to a lasagna filling I make with the ricotta, spinach and sauteed mushrooms.

I would add it - grated very finely and also not as much as called for.

I always add nutmeg to ricotta dishes, and spinach dishes too.

I always omit nutmeg in ricotta dishes and spinach dishes - it ruins the flavor of the spinach for me, and then I can't eat it. I generally only use nutmeg in sweet dishes, and so I might add it to ricotta if I were putting that in canoli. I might add a tiny amount of nutmeg to a Middle Eastern, Indian, or African spice mix, but I always reduce the amount until I taste it.

I think that if you use fresh oregano, you won't need the lemon, but if you use dried, the lemon zest might perk it up a bit. I would be inclined to use a smaller amount. In the end, if you think it is missing something, you can add a bit of lemon juice to the final dish, if you think it needs the lemon flavor.

It's fine to omit anything that you strongly dislike.

Lars, I think I am nutmeg sensitive. Small amounts jump out at me, so I agree, I only it in sweet dishes too.

This is a funny one! I'm fine with nutmeg in traditional béchamel for savory dishes (though non-funky or aged dairy is sweet), but in sweets I find more than a tiny bit of it cloying! I also think it's cloying as garnish, especially on rich drinks. Whereas, I'm okay with a moderate amount of Ceylon cinnamon, which is mild, in meat dishes—but not Saigon cinnamon, which is stronger and harsher. (This is the ”true” cinnamon vs. cassia thing, but I'm super picky and only like either of them from these two, whose names stay, even though the locations aren't called that anymore.)