Combine the coconut milk, natural sugar, vanilla, cinnamon, sea salt, and 4 cups water in a 4-quart saucepan over medium-high heat.
Stir gently to dissolve the sugar. Bring to a boil.
Stir in the oats, simmer for a minute or two, then remove the pan from the heat. Let cool at room temperature until tepid, then cover and refrigerate overnight.
When ready to eat, bring the oatmeal to a simmer over medium heat and cook, stirring occasionally, until thick and the oats are tender and chewy (~ about 10 minutes)
Off the heat, stir in the reserved marinade.
Top with the peaches, pecans, and chia seeds, if using. Drizzle with a little extra milk, and serve