Final answer:
Lentils, being part of legumes, are the best vegetarian source of zinc mentioned, whereas spinach, milk, and beef are not as rich in zinc for vegetarians.
Step-by-step explanation:
The best source of zinc for a vegetarian, as included in the teaching by the nurse, would be from lentils. Lentils are part of the legumes family, which are known to be good sources of zinc. While other options like spinach and milk do contain zinc, they do not have as high a concentration as lentils. Despite beef being rich in zinc, it is not suitable for vegetarians. Foods such as almonds, enriched breads and cereals, and dark green leafy vegetables are also valuable sources of zinc for those on a vegetarian diet.