When I lived in Sth London the Brixton market wasn't too ar away. Out here in mid-Wales I sometimes miss access to 'ethnic' stuff but I had to go into Birmingham yesterday and walked to the open market. I was very impressed with the quality of fruit and veg - worth the trip just for that. Any how I did buy hal a breadfruit and some green plantain.
Plantain: I like it simply peeled, sliced into long bacon-like strips and fried. If you prefer a sweeter taste then wait until the plantain starts to yellow before cooking but my preference is green.
Breadfruit: This has a pithy middle so cutting is a bit like preparing melon... slices and the pithy bit removed and peeled. Options then are again simple slice thin and fry or chunk and sautee. Traditionally breadruit was baked in a fire pit (like spuds on fireworks night) and can be done simpler by wrapping chuncks in foil. It's just a carbohydrate with an intersting accent to it's lavour, You can treat chunks like a potato. Baked left-overs can by sauteed or brekkie.
It's also worth chatting to stall-holders for recipe ideas when you find something you don't know how to handle.
For a nice brekkie a couple of slices of fried plantain, a strip of bacon, a couple of johnny cakes (fried dough balls) and a chunk of water-melon.