Answer

The commandment of forgotten produce is not a commandment to forget, but to leave in the field (not to take) what was forgotten. There you can certainly have intention.
But the question is also phrased imprecisely. There is no such thing as fulfilling a commandment through mere forgetting, regardless of the rule about whether commandments require intention. Such a case is parallel not to an unintentional act, but to mere involvement without awareness. A commandment is always fulfilled מתוך awareness and a decision to fulfill it, even according to the view that commandments do not require intention.