Combine 2 cups rolled oats, 2 cups almond milk, 1 cup Greek yogurt, and 1/4 cup honey in a large mixing bowl. Whisk thoroughly until the mixture is well blended and no lumps remain, about 2 minutes.
Add 1 tbsp vanilla extract, 1 tsp cinnamon, and 1/2 tsp sea salt to the oat mixture. Stir everything together until the spices are evenly distributed throughout.
Gently fold in 1 1/2 cups blueberries, 1 1/2 cups strawberries, and 1 cup raspberries into the oat base. Reserve a handful of whole berries for topping if desired.
Divide the summer berry overnight oats family recipe evenly among four mason jars or containers. Press down gently so each serving is compact and the liquid covers the oats. Seal containers and refrigerate for at least 8 hours or overnight.
Remove from refrigeration and check consistency. If the texture seems too thick, stir in 2-3 tbsp of almond milk per serving until reaching desired creaminess.
Top each jar with 1 tbsp sliced almonds, 1/2 tbsp flaxseed, 1 tbsp shredded coconut, and 1/4 tbsp chia seeds. Lily always adds extra almonds to hers for extra crunch.
Serve chilled directly from the jar or transfer to bowls. These berry breakfast jars can be eaten cold or gently warmed in the microwave for 60-90 seconds if preferred.