TheFork users who ate in Winterthur have said really good things about 70/30, Punto 9 and Jalapenos Mex. Maybe you should give them a try!
Some of the more popular good for families restaurants well suited for a business lunch in Winterthur according to TheFork users include:
Punto 9, with a 9.8 rating
Jalapenos Mex, with a 8.3 rating
NA081 Glattbrugg, with a 9.2 rating