What type of work will be involved? Is there some theme you would like to reinforce through lunch like Edna's Restaurant, 3715 W. Madison where people get a second chance? Possibly Epic burger or Soul Vegetarian East where the food is natural and the business plan socially responsible.
I imagine any of these places would be more than helpful if you were to call and make arrangements.
Also, as you can glean from reading the board or even from the title many persons have a great affinity for Chinatown. 40 people is very feasible for many locations and I am sure it would be a memorable experience for your group.
Good Luck
“Statistics show that of those who contract the habit of eating, very few survive.”
George Bernard Shaw, Irish playwright (1856-1950)