Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper or use a silicone baking pan.
In a large bowl, whisk together the plant-based milk, maple syrup, vanilla, ground chia seeds and ground flaxseeds. Let sit for about 5 minutes to allow the chia and flax to hydrate.
Add the oats, cinnamon, baking powder, salt, if using, and pecans. Stir until well combined.
Dice 1 cup of the peaches and gently fold them into the oat mixture.
Pour the mixture into the prepared baking dish and spread evenly. Slice the remaining 1 cup of peaches and arrange over the top.
Bake for 35–45 minutes, or until the oatmeal is set in the centre and lightly golden around the edges.
Allow to cool for 5–10 minutes before serving.