Combine all the ingredients (except for the optional toppings) in a jar and stir until well combined.
Refrigerate for at least 4 hours or overnight.
Top with slices of banana, crushed peanuts, and a drizzle of peanut butter just before eating if desired.
Store in the refrigerator for up to 2 days.
Video
Notes
Nutrition facts are an estimate and do not include toppings (extra banana, peanut butter, or peanuts). Since this overnight oats recipe includes mashed banana, it doesn't last as long in the refrigerator. It's best eaten within 24 to 48 hours, or the banana will start to develop an "off" taste.