Trim the roots and greens off the leeks. Thoroughly wash the remaining white stems, and slice them in 3 cm or 1 inch thick rounds.
Heat up some olive oil in a skillet on medium heat. Place the sliced leeks in the pan, and fry for 5 to 7 minutes. Turn them and fry for 3 more minutes. Each side should have a dark-ish brown color.
Add ⅓ cup vegetable stock or water to the pan, cover the pan, and simmer the leeks for 5 to 7 minutes, or until the liquid has evaporated.
Add the miso paste, fennel seeds, salt, pepper, and a splash of water (about ¼ to ⅓ cup) over the simmered leeks. Swirl the pan around and simmer everything until the liquid goes from a watery consistency, to a glossy one. This will take 3 to 5 minutes.
Plate the glazed leeks with lemon zest on top, lemon juice, flaky salt, freshly ground black pepper, and pistachios or sesame seeds.
