Beans on toast can be a healthy and nutritious snack if you choose the right ingredients. I myself prefer wholemeal bread - I never usually eat white bread if I can help it. I also do not butter my toast - absolutely no need for extra fat. Try and choose beans that are low in salt and sugar and you have a quick and tasty snack anytime of the day.
These days though, I don't eat beans on toast often, I usually have the beans as an accompaniment to the Great British Breakfast (if I cook it's usually lean grilled bacon, scrambled eggs in olive oil, grilled tomato and grilled black pudding and of course baked beans) which I indulge in about once a month.