The people doing the harvest on this Hualien (花蓮) street (below) told me it was breadfruit, but it looks more like durian. Well, maybe it's overripe breadfruit -- I'm no expert, but breadfruit seems to be smaller if not harder. It's not this juicy.
I googled breadfruit and got the following at wiki: "Ancestors of the Polynesians found the [breadfruit] trees growing in the northwest New Guinea area 3,500 years ago. They gave up the rice cultivation they brought with them from Taiwan and raised breadfruit wherever they went in the Pacific (except Easter and New Zealand, which were too cold)."
If this is correct, breadfruit was then, ironically, introduced to Taiwan by the Dutch after they got it off the ancestors of the Taiwanese. I don't think there were any breadfruit in Taiwan before the Dutch. Here's Reverend George Canadidius' (the pioneer missionary) description of Taiwan's agriculture from 1624: "Three kinds of fruit are cultivated -- of which the first is called ptingh, the second quach, and the third taraun, which is very much like our millet -- besides two kinds of vegetable somewhat resembling our Dutch beans, with three kinds of bulb which they use instead of bread, so that if bread, rice, or other fruits were wanting, they could subsist entirely on these bulbs. The island also produces ginger, sugar-cane and melons [I don't think breadfruit counts as a melon though], but the people plant just sufficient for their wants. Bananas, cocoa-nuts and pinang are found in great abundance, with some other kinds of fruit which are not of great importance, and the names of which I am unable to pronounce in our language. This is all that their fields and gardens produce for sustaining their bodies."
In later reports, the Dutch also later claimed they introduced breadfruit, along with other crops, to Taiwan. The word for breadfruit in Dutch is breadfruit. Someone on a previous post told me that the Aboriginal word for breadfruit is bat-chit-l'ut 八支律 , which sounds like a transliteration for breadfruit. If the aboriginal people had breadfruit prior to 1624, they most certainly would have had their own name for it. Who knows? Maybe this is the word an aboriginal tribe unfamiliar with breadfruit adopted later on. But it seems unlikely, especially if we consider Taiwan's small size or trade, that an important crop would remain undetected by certain groups.