Glad to meet you, and welcome to BYC. Leafy greens are terrific, from dandelions and common plantain (without pesticides, please!) to mustard, kale and lettuce, are great all the time.
I give my ladies kale over the winter, and start a greens garden for them each spring. Here's a link on gardening for chickens that includes links to other related articles and a list of the DO NOT EAT plants.
They LOVE a scratch mix I put together that includes black oil sunflower seeds, a store-bought scratch mix, and black soldier fly larvae. BUT they can only have a little of that. So I make it the "come home" treat to get them back in the pen when it's time.