Mix the milks. In a medium bowl or large measuring cup, whisk together the evaporated milk, whole milk, and sweetened condensed milk until smooth.
Stir in the vanilla, cinnamon, and a pinch of salt.
Add the yogurt. Whisk in the Greek yogurt until the mixture is creamy and well combined. Taste and adjust sweetness with a little more condensed milk or a drizzle of maple syrup if needed.
Combine with oats. Add the rolled oats to a large jar or container. Pour the tres leches mixture over the oats and stir well so every oat is coated.
Chill overnight. Cover and refrigerate for at least 4 hours, preferably overnight.
The oats will absorb the liquid and thicken to a pudding-like texture.
Stir and adjust. In the morning, give the oats a good stir. If they’re thicker than you like, loosen with a splash of milk. If you want more sweetness, add a touch more condensed milk or honey.
Top and serve. Spoon into bowls or keep it in the jar.
Finish with sliced strawberries, a sprinkle of cinnamon, toasted coconut, or a small dollop of whipped cream for a true tres leches feel.