There was a missed opportunity in the show to depict how the Lion Guard met each other.
The closest we have to an origin story is the flashback in S3 when Kion and his friends rescued an un-born Ono. But by then, Kion had already known Bunga, Beshte, and Fuli.
We could've had an origin story about how they met, and whether or not their first encounter was before or after Kiara's meeting with Kovu.
But alas, we may never see that happen :(