Teaching job

Welcome to the forum! You can find a lot of information here by using the magnifying glass up top.
Working in Belize is not any easy or simple process. This is the general guideline -
"Do you wish to settle and work in Belize? Unemployment is high, so there are a number of jobs that are reserved for Belizeans only. In fact, in order for an employer to hire a foreigner, they must show that Belizeans are unable to do the job. If you have a special skill, you may be able to find a job.
The other way to get a work permit is to start a business. The government is much more friendly with this route, particularly if you plan to hire Belizeans and create new jobs." For more specific details, go to the  website for the Ministry of Labour of Belize.
I can't tell you if there is a specific need for teachers on Ambergris. You could try to assess that from a Facebook post, as there are a number of Facebook groups on Ambergris/SanPedro. Most people coming to Belize are either retiring,  or don't need to work. Getting employment would not be easy, and the wages in Belize are really low compared to the US.
Hope you find what you are looking for.