Is that in its raw state, cut open, with the seeds inside showing, or has it been cooked and stuffed with sultanas?

In the raw state. The red seeds don't taste of anything very much.

It looks as if it has just come out of the deep fat fryer! Could it be a type of gourd?

The yellow outer is quite soft and overnight it opened to the amount shown. Before that it was hardly open at all.

Found it!
Momordica charantia, otherwise known as bitter melon

Thank goodness, I couldn't find it at all. Not worth eating?

Seemed pretty tasteless, though I read the seeds are sometimes used in a salad a bit like pomegranate - Turkish name seems to be 'strong pomegranate' but it seems it is a herbal recipe. In Wikipedia it has
'In Turkey, it has been used as a folk remedy for a variety of ailments, particularly stomach complaints. The fruit is broken up and soaked in either olive oil or honey.'
Don't think I'll try it though.

Hmm, doesn't sound particularly tasty!