Serializing assets field is returning a serialized criteria object, but how to return serialized data?

Question

I'm saving a custom element that has content by field layout.
When successfully saved, I return the object in the response.
Now, most of the data is usable but the assets field is just a serialized criteria query.

return $this->asJson([
    'success' => true,
    'quotation' => $quotation
]);