Late answer (I'm new here), but I'll also try to provide my take on this question.
I think it would be easier to say this if we translate the words "too" and "not enough" first.
Too - Masyado
Not enough - Kulang
Now let's try to translate the whole sentence:
The food is too plain.
Masyadong simple yung pagkain. (or honestly, just say "Masyadong plain yung pagkain." Most people use Taglish anyway and there are some words where the English word is used more than its Tagalog counterpart.)
The food has not enough flavor. (Had to change "is" to "has" because the verb needed to be a possessive verb to have correct grammar.)
Kulang ng lasa yung pagkain. (It's also common to say "Kulang ng flavor yung pagkain" instead. I think common English words are also common in Taglish, if you're not a purist in your learning of Filipino.)
Hope this helps!