It really shouldn’t be, but the game treats it as one. For example, the Cleric Forge’s Channel Divinity blessing.

You conduct an hour-long ritual that crafts a nonmagical item that must include some metal: a simple or martial weapon, a suit of armor, ten pieces of ammunition, a set of tools, or another metal object.

This is more specific than the general rule

For the purpose of these rules, an object is a discrete, inanimate item like a window, door, sword, book, table, chair, or stone, not a building or a vehicle that is composed of many other objects.

So in the case of armor, it counts as one object even though it’s not a discrete item. But unless there’s something calling a feast one object, it follows these rules.

If you allow a feast, what doesn’t count as “one object”?

You can only make one object. I could understand if it was a big pot of soup, but I don’t see how this counts as one object.

Here’s how I’d use Fabricate to cook:

1. Fabricate plate mail.
2. Sell the plate mail.
3. Use the money to hire a chef.