Preheat oven to 350 F. Warm the stock or broth in a pot on low.
Clean the leeks by slicing them in half lengthwise, then thinly slice and soak in cold water to remove dirt. Drain.
Strip the chard leaves from the stems, chop into ribbons, and chop the stems thinly.
In a Dutch oven, heat olive oil and 2 tablespoons of butter on low. Add leeks and chard stems, cooking until soft (about 10 minutes).
Add rice to the pot, stirring constantly for 2 minutes to coat.
Add 4 cups of broth and chard leaves, stir to incorporate, then bring to a boil.
Cover tightly and place in the oven for 20-25 minutes until rice is cooked through.
Remove from oven, place on low heat, and stir in peas, Parmesan, lemon zest, remaining butter, and additional broth to desired consistency.
Season with salt and pepper, serve with more Parmesan.
