Prepare your peaches. If using fresh, wash, halve, remove pit, peel, and dice into ½ inch cubes. For frozen, thaw and drain. For canned, drain and rinse if packed in syrup, then dice.
In a medium mixing bowl or directly in your mason jar, combine the rolled oats, milk, Greek yogurt, chia seeds, honey, vanilla, cinnamon, and a pinch of salt. Stir thoroughly until no dry pockets remain.
Reserve about one-third of the diced peaches for topping. Fold the remaining two-thirds into the oat mixture and stir gently to distribute evenly.
Spoon the mixture into one or two mason jars, pressing down to eliminate air pockets. Leave about 1 inch of space at the top for the reserved peaches. Seal tightly with the lid.
Refrigerate for a minimum of 4 hours, but overnight (8-10 hours) is best for the oats to fully absorb the liquid and for the flavors to meld.
In the morning, remove the jar from the fridge and stir the oats thoroughly. Add your reserved fresh peach pieces on top and add any extra toppings like granola, almond butter, or fresh mint. Enjoy cold or warm.