For Westerners to find work in Nepal is next to impossible. Local employment is high and industry very limited. There are a very limited number of work opportunities that include with airline offices, trekking agencies, aid groups, consultants or travel. The easiest and most promising job option is teaching English. There are some number private schools with demand for English teachers however, the compensation is extremely low. Qualified masseurs and yoga/meditation instructors might have somewhat better luck when it comes to finding work at slightly better compensations. Most of the work being done by foreigner in Nepal is of voluntary type.
It is against the law to work on a tourist visa in the country, despite a few people take jobs as guides. This not only raises questions of ethics, where you are taking a job that a local Nepali is better qualified to handle but if caught you will be punished severely.
To be able to work legally in Nepal you must get a non-tourist visa. Even unpaid work requires that you get such a visa. Typically this is arranged before one enters the country. Switching from a tourist visa to a work visa, after you enter the country is hardly ever allowed. A work permit has to be applied for by the employer and the potential employee must leave the country during the time paper work is being completed. The process is rather tedious and can end up taking several months.