Preheat oven to 320°F/160°C. Line a baking sheet with parchment paper or a silicone baking mat.
Blend dates in a food processor or mash with a fork to form a paste, adding water as needed.Tip: If your dates are very hard/dry, soak them in hot water for 10 minutes first. Drain well then add to a food processor or mash.
Add peanut butter and vanilla extract and mix to combine.
Transfer date mixture to a bowl with oats, seeds, and cinnamon. Stir well to combine.
Spread date mixture outon a lined baking sheet. Press down with a spatula to compact the granola (this helps the granola form clusters).
Bake for 15-20 minutes until the edges start to brown, then carefully flip the granola (break it apart into large sections so it's easier to flip). Bake another 10 minutes, then stir and check the granola every 5 minutes and remove any pieces that are browning too quickly. (It should take about 40 minutes total to bake.)
Remove the granola when it's golden-brown. It will still be a little soft right out of the oven, but it will crisp up as it cools.
Let the granola cool on the baking sheet, then break into clusters and store in an airtight container at room temperature.