The gourd you might be thinking of is the Japanese "pumpkin" or Kabacho.

I love this grilled over high heat - it is better than acorn or
butternut squash in that it has more complex texture and higher sugar
content. When I first had it there were no places to buy it in my city
- now, most Asian markets stock them - although the quality varies quite
a bit.

Is bitter gourd ever used in sushi?

Thanks,

Rick