Ah, so you can say either "Mi non piace..." or "A me non piace..."
EDIT: As ZuMako8_Momo pointed out below, it's "Non mi piace" not "Mi non piace".
Yes, either «Non mi piace il cioccolato.» or «A me non piace il cioccolato.», or even «Non piace il cioccolato a me.» I believe.
"A me" emphasizes the me, making it sound more like "I, rather than someone else, do not like chocolate."
To me non-pleasing is the chocolate - is the literal translation, but not how you would say it in English.
"Chocolate is not pleasing to me," but since no one says that, it is best to translate the sentence as "I do not like chocolate."
Italian tends not to repeat pronouns. If you already have «a me», you do not need the «mi», and vice versa. Now in Portuguese and Spanish on the other hand, that happens quite frequently, the repetition of the two pronouns.
"Piace" doesn't actually mean "he likes" or "she likes", it means "it is pleasing". "Piaccio" means "I am pleasing".
Non piaccio al cioccolato - I'm not pleasing to chocolate / chocolate does not like me
A me non piace il cioccolato - The chocolate is not pleasing to me / I don't like chocolate