CRUSH strawberries to a chunky purée with a potato masher in a large bowl. It should measure about 5 cups.
COMBINE sugar, pectin and zest in a medium bowl. Sprinkle over the strawberries and stir to combine. Let stand for 3 min, then stir well.
LADLE into 6 clean 1-cup canning jars, leaving ½-in. headspace from rims. Wipe rims clean, then secure lids tightly. Let stand for 30 min. Jam will be very softly set. Refrigerate up to 1 week or freeze up to 1 year.