Your other option is to split up your lunchtime and do a later but more hearty morning snack and then go outside and then come in, get washed up and have more to eat - for sure a drink, and the rest based on what was served/eaten before - do the meal in two stages. Then do nap right after as you do now.

Once our deck goes in we will be doing an outside time just after everyone is here and then back in for snack and morning naps to start. We go out after nap/snack and stay out till parents pick up so for some it is only 15-20 minutes but not my problem since it is an hour to an hour and a half for most of them. It means all the sand and mud and dirty kids go home not back into my house - love it this way.

In winter we do go outside at noon as that is the warmest part of the day and often it is my daughter who comes over after work - works mornings only and takes out those that can actually walk to play in the snow and I stay in the house with the babies. Lunch from 11-12, outside 12 - 12:30 then diapers and in bed for 1.