While odds are good that Monty's lesion is likely a viral papilloma, the only definitive way to determine what's causing the lesion is through removal and biopsy. Viral papillomas are most common in young dogs (like Monty), as well as those that are immunosuppressed. While viral papillomas are contagious between dogs, in young dogs they typically resolve without treatment. That said, some do dramatically worsen or become infected, which is a bit more complicated to manage. Topical treatment won't do any good, particularly for any lesion in the mouth. It would be best to have this lesion evaluated by your vet, who may recommend diagnostic testing to confirm their diagnosis. With that said, it's also not wrong to continue monitoring it to see if more lesions develop or if this one changes at all before pursuing further investigation. Until you know for sure what is causing this lesion, keep Monty away from other dogs at doggy daycares, dog parks, or kennels. I hope that everything goes well!