Never seen this before. Could you tell me why? Plant was large with lots of leaves.
Zucchini Plant Produced Only One
Certified GKH Gardening Expert
It sounds like you may have had a pollination problem. This article will help: https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm
Did you have other blooms on the plant? If not then you may have used too much nitrogen when fertalizing. This causes beautiful plants but no fruit (vegetable).
If you had a lot of blooms, male and female, then the problem was pollunation. Polunation is something you can do by hand, with a feather, q-tip, or small paint brush.
Whatever article you use can be rolled around inside the male bloom, coating it with pollen, then touch the inside of the female bloom a couple of times depositing a small amt of pollen. Might do a trial and error run..