Rinse the poblanos and dry them. Turn on the broiler. Place peppers on a sheet pan and broil for a few minutes, flipping once, until both sides are roasted. Remove and place in a large covered casserole dish (with the cover on) to cool and steam. Make sure it's large enough to hold the peppers in one layer as you'll be using it next. Once the peppers have cooled, remove from the dish and remove the charred skins carefully. Cut in half and remove seeds and interior stem / membranes. Wipe out the dish to use again in a future step.
Bring a large saucepan of water to a boil with plenty of salt. Add the farro and cook for 15-25 minutes, until cooked. Drain well and shake to get most of the liquid out.
Meanwhile, soak the walnuts in hot water for 10 minutes. Drain and dry. Chop roughly.
Preheat oven to 350ºF. Oil the dish you cooled the peppers in. In a large bowl, mix cooked farro, diced cheese, chopped walnuts, 1 cup passata and most of the paprika. Season to taste with salt and pepper.
Fill the peppers with the farro mixture. It can overflow some if you have a lot of material. Cover, place in the oven and bake 15 to 20 minutes, until peppers are tender.