Add frozen berries to a medium saucepan, or pot, over medium-low heat. Cook, stirring occasionally, until thawed and releasing juices (about 5–7 minutes).
Stir in the sugar, lemon juice, lemon zest, and a pinch of salt.
Bring to a gentle boil, then reduce to a steady simmer. Cook for 15–20 minutes, stirring occasionally, until thickened.
Use the back of a spoon, or spatula, to break down the berries to your desired texture.
Continue cooking until the jam coats the back of a spoon.
Remove from heat and let cool completely (it will thicken further as it cools).
Transfer to a jar, finish cooling completely, and refrigerate.