Dietitians are certainly promising, not only in large canteens, but also in high-end hospitals, nursing homes, kindergartens, primary schools and other institutions. But high-end positions also require high diplomas, at least undergraduate courses. If you only have a high school education or a trained adult college, it will be more difficult to find a job in the future, because ordinary canteens are unwilling to have this position. If necessary, they will arrange their own training with nutritionist's certificate to cope with it, and rarely go there specially.

Suggestion: Try to continue studying, at least take a junior college exam first, and then get an undergraduate diploma.