Rinse all 3 peaches, cut in half, twist to separate, and remove the pit. Roughly chop 2 peaches for the blender and dice the remaining peach into small, even pieces, splitting the diced peach into two portions: one to fold in now, one to save for topping.
Add the 2 roughly chopped peaches to the blender along with the milk, maple syrup, vanilla, cinnamon, and salt. Blend for about 20 to 30 seconds, until smooth and the base looks like a thin, pale peach shake.
In your mixing bowl, add the rolled oats, chia seeds, and Greek yogurt. Stir them together briefly so the yogurt starts to coat the oats and the chia seeds stay separated.
Pour the blended peach base into the bowl with the oats, chia, and yogurt. Stir well for a full 20 to 30 seconds, scraping the bottom, until there are no dry pockets and no clumps of chia. Fold in the first portion of diced peaches and taste, adding a little more maple syrup if your peaches were on the tart side.
Divide the mixture evenly between 2 jars or lidded containers. Give each jar one more quick stir so the chia does not settle, then seal and refrigerate for at least 6 hours, ideally overnight.
In the morning, stir each jar and loosen with a splash of milk if the oats are thicker than you like. Top with the reserved diced peaches, a few chopped toasted pecans, and a light drizzle of maple syrup, then eat cold straight from the jar.