Mix oats, chia seeds, oat milk, and vanilla yogurt together in a large cup, jar, or container.
Mix again after three minutes to break up any clumps forming. Cover and refrigerate for at least 1 hour, ideally overnight.
Stir again before serving and adjust consistency with extra oat milk if needed.
Notes
Adjust oat milk depending on desired consistency—add more if too thick, or an extra scoop of chia seeds if too runny. Store in a sealed container in the fridge for up to 4 days. Stir before serving.