You want to tell him about all of the amazing food that they had at the party, so you say this.
In casual English, "a spread" is a big table
full of food that's
being offered to guests at
a party, a conference, for holidays, etc. This phrase brings to mind the
picture of lots of different dishes spread out over a table. Use it like
this:
Look at this spread! Oh my goodness,
it must have taken you forever to cook all this.
They've got a pretty decent spread
here tonight.
This is a phrase that means
something like "a lot", "unbelievable",
"amazing", or "horrible". Use it in casual speech when you're pretty excited or annoyed by
something:
I have a pile of backed-up paperwork
to take care of like you wouldn't believe!
This means "I have a huge pile
of paperwork."
She's got artistic talent like you
wouldn't believe.
This means "She's amazingly
talented".
You can use "like you wouldn't
believe" after a noun, as in the two examples given above. And you can also
use it after a verb like
this:
The soil here is great. The tomatoes
have been growing like you wouldn't believe.
You should use "like you
wouldn't believe" in casual spoken English, when you feel really energetic
and you want to not only communicate your message, but also entertain your
listeners. For example, it's good to use when you're telling a story.