If the Medjool dates are not very soft, cover them with hot water for 5 minutes, then drain and pat dry. If using Deglet dates, soak for 15-20 minutes.
Place the oats in the bowl of the food processor and pulverize them until you have a fine oat flour.
Add the pitted dates, peanut butter, maple syrup, vanilla, and salt to the oat flour. Pulse until the mixture forms into a sticky dough. If it feels too dry, add a spoon of plant-based milk (or more maple syrup), a teaspoon at a time until the dough just sticks together when pressed.1. NOTE: If the dough is too sticky to handle with your hands (this is more likely if your kitchen is warm), place the dough in the fridge for 20 minutes to firm it up a bit.
Line a 8x4- or 9x5-inch loaf pan (20x10 cm or 23x13 cm) with parchment paper, letting the excess hang over the long sides to form a sling. Spread the dough into pan and smooth the top out evenly, pressing all the way into corners with your fingers. Use a flat-bottomed glass to get the mixture even on top. Place the pan in the freezer for 30 minutes (or longer) to set.
Before removing from the freezer, warm the jam up in a saucepan over medium-low heat to make it a bit runny (if using homemade chia jam, this step should not be necessary). Pour the warm jam on top of the dough in the pan, spreading out with a silicone spatula. Add more jam as desired.
Return to the freezer to set. Then slice into 8 thick bars or into small squares, and serve immediately. Store leftovers in the freezer.