Line a 9-inch square baking pan with one strip of parchment paper, cut to fit neatly across the base. The parchment paper will make it easy for you to slice the bars later.
For maximum flavor, toast the pecans. In a medium skillet over medium heat, toast the pecans, stirring frequently (don’t let them burn!), until they are nice and fragrant (about 4 to 7 minutes). Transfer them to a cutting board to cool. Set aside 16 of your prettiest pecan halves for garnish, then chop the rest. Set aside.
In a large mixing bowl, combine the oats, cinnamon, and salt, and stir to blend. Set aside.
Pour the liquid ingredients into the dry ingredients. Use a big spoon to mix them together until the two are evenly combined and no dry oats remain. Add the chopped pecans and stir until they are evenly dispersed. The drier the mixture, the more firm the bars will be, so stir in extra oats if the mixture seems wet. Conversely, if you used a super-thick nut butter, you might need to drizzle in another tablespoon of maple syrup or honey to help it all stick together.
Transfer the mixture to the prepared square baker. Use your spoon to arrange the mixture fairly evenly in the baker. Cover the bottom of a flat, round surface (like a short, sturdy drinking glass) with a strip of parchment paper and pack the mixture down as firmly and evenly as possible. Press the reserved pecan halves into the surface to create 4 even rows and 4 even columns.
Cover the baking pan and refrigerate for at least one hour, or overnight. This gives the oats time to absorb moisture so the granola bars can set. When you’re ready to slice, lift the bars out of the baker by grabbing both ends of the parchment paper. Use a sharp chef’s knife to slice the mixture into 4 even rows and 4 even columns (these “bars” stick together better in a square shape).
For portability, you can wrap individual bars in plastic wrap or parchment paper. Bars keep well for a couple of days at room temperature, but I recommend storing individually wrapped bars in a freezer-safe bag in the freezer for best flavor. They’ll keep for several months in the freezer.