In a large bowl, combine the oats, protein powder, chia seeds, and salt. Add the milk, maple syrup, and vanilla and stir until fully incorporated.
Divide the oats mixture evenly among 4 containers or jars with lids. Refrigerate at least 6 hours or overnight. Keep the jars refrigerated until serving.
Top each jar with ½ cup of Greek yogurt and mini chocolate chips or marshmallows (if using) to serve.
