Making dessert doesn't get much easier than this. Be sure to use a 6-quart (or larger) cooker as this gets very foamy, which can clog the vent or cause spewing liquid in a smaller pot. Make a double batch if you have enough room; it's that good.
Place the tapioca pearls in a fine mesh strainer and rinse under running water for 30 seconds.
Add the milk to a pressure cooker. Add the tapioca and salt, if using, and stir. Lock the lid. Bring to a high pressure; cook for 4 minutes. Let the pressure come down naturally. Quick release any remaining pressure after 20 minutes. Open the lid carefully, tilting it away from you.
Stir in the sugar, vanilla, and lemon zest.
Spoon 2 tablespoons berries into the bottom of 4 pretty bowls or parfait glasses. Add about 1/4 cup tapioca, then 3 tablespoons berries. Add another 1/4 cup tapioca and top with berries. Garnish with mint.
Variation: If stone fruits are in season, substitute chopped stone fruit for the berries.