Why would it be? Tumhe is familiar singular, which is what the हौ is referring to - not the bananas.
तूम्हें is actually dative. With पसंद the subject is always the thing that is liked (in this case bananas) and the person who likes it is in dative.
"to you" is dative. However, if "bananas" is subject and plural, why isn't the verb plural? Is it possible that "pleasing" is subject with a singular verb in agreement and that "bananas" is (sorry for the Latin grammar) epexegetic to the supposed "it" of the verb? Please note that I'm guessing here - any Hindi gramarians lurking about? Note that Marcin85 does not answer the question that was asked concerning the number (sing/pl) of the verb. This is also my question.
This is an edit: I notice that other similar sentences use the plural form of the verb; I suspect that the singular use in this sentence is simply a typo. (But I did have fun trying to concoct the new observation above. Mea culpa.)
I actually raised the question concerning the number. As you say, bananas is plural subject so the verb should be also plural, that is हैं.