Line an 8-inch square pan with parchment paper, leaving an overhang on two sides.
Remove all pits from the dates.
If the dates are firm or dry, soak them in warm water for 10 minutes, then drain thoroughly.
Add the rolled oats and walnuts to a food processor.
Pulse several times until the walnuts are chopped and some of the oats are broken down while plenty of oat texture remains.
Add the dates and pulse until broken into small sticky pieces.
Add the peanut butter, vanilla, cinnamon, salt, and optional chia seeds.
Process until the mixture begins to clump together.
Pinch some mixture between your fingers. If it does not hold together, add 1 tablespoon of warm water and pulse again.
Transfer the mixture to the prepared pan.
Press down very firmly and evenly using the bottom of a measuring cup or glass.
Refrigerate for at least 1 hour.
Lift the chilled mixture from the pan using the parchment paper.
Cut into 12 bars.
Store refrigerated until ready to serve.