In a well-greased 3-qt. slow cooker, combine the first 6 ingredients. Cook, covered, on low until oats are tender, 7-8 hours. Stir in peaches just before serving.
Pressure cooker option
Decrease water to 3 cups. Add to a 6-qt. electric pressure cooker coated with cooking spray. Stir in oats, soy milk, brown sugar, salt and vanilla. Lock lid; close pressure-release valve. Adjust to pressure cook on high for 4 minutes. Let pressure release naturally. Stir in peaches just before serving. Oatmeal will thicken upon standing. If desired, top with optional toppings.