Smokey Lemony Peas and Carrots

6 oz. sliced good quality bacon, cut crosswise into ½” pieces1 red onion, thinly sliced1 lb. fresh or thawed frozen English peas1 T. finely chopped tarragon, more for garnishZest of 1 lemonKosher salt, black pepperCrushed red pepper flakesJuice of 1…