To be correct the sentence would be: "My favorite fruit in (or during) the fall season are peaches." I would use during instead of in (although this is my opinion). You could also say, "My favorite fruit to eat during fall are peaches", but that kind of changes the meaning slightly. But as for the 'is', you would use are. So, "My favorite fruit during the fall season are peaches."

I can understand why this is a little confusing. "Fruit" here is an uncountable word which grammatically is a singular concept and so must take "is" and not "are". However, a singular concept can be described as being equivalent to a plural concept, (normally using the verb "to be") like it is here.

yes, you are right , cheers :)

My favorite fruit in the fall ( autumn ) are peaches.