I grow breadseed poppys for their beauty and their history as do several thousand other gardeners in Europe and the U.S. They really are quite lovely early in the summer, especially as a mass planting of the untampered single varieties with variable white to pink to lavender blossoms. The singles I grow have been sent to me over the years with notes such as, "my great grandma brought these seeds over from Poland in the early 1900's". There are beautiful doubles, scarlet reds and so many other varieties of the breadseed poppy, Papaver somniferum but it is the heirloom ones I most enjoy growing. Yes the species, somniferum is quite the opposite of insomnia. It is the sleep-inducing opium poppy.
I presume that Grandma from Poland was using the seeds in baking. My friends who raise the breadseed poppy in larger plantings than I do collect the seeds for use in baking as an alternative to buying the mostly irradiated seed that you see on sale in the supermarket (irradiated seed will not germinate and some folks just don't like consuming irradiated food). While ingesting a lemon poppyseed muffin is not going to result in a narcotic "high", the heaping spoon of seeds in it can cause one to test positive for opiates on a drug test.
Papaver Somniferum, is a hardy annual that grows especially well when sown thinly in the early spring in full sun and then flowers a few weeks later when the days are long in June. The fragile flowers don't last long but it's pods are often dried and used in flower arrangements. One of the nice characteristics of the Breadseed Poppy is that the capsule dries sealed therefore preserving the seeds inside instead of opening and shattering the seeds before they can be harvested.