Preheat the oven to 160°C (325°F).
Line a baking tray with parchment paper.
Add oats and chopped pecans to a mixing bowl.
Pour in maple syrup.
Add oil or melted butter.
Stir in vanilla extract and salt.
Add cinnamon if using.
Mix until everything is evenly coated.
Spread the mixture evenly on the baking tray.
Lightly press the mixture down with the back of a spoon to help form larger clusters.
Bake for 20–25 minutes, stirring halfway.
Remove once golden and fragrant.
Cool completely on the tray without stirring so the clusters can set and become crunchy.