Line a baking sheet with parchment paper or use a shallow container for chilling. Set aside.
Combine the rolled oats, protein powder, cinnamon and sea salt in a large bowl. Stir with a spoon to evenly distribute the powder and spices.
Place the peanut butter and honey in a microwave-safe bowl and heat for 12–15 seconds to loosen (or warm gently on the stove). Add the vanilla and stir until smooth.
Pour the peanut butter mixture over the dry ingredients. Fold everything together with a sturdy spatula until the mixture holds together but still looks slightly crumbly; use your hands to finish mixing if needed.
Gently fold in the mini M&Ms, chocolate chips and peanut butter chips so they’re distributed but not crushed. Press a handful together—if it’s too sticky, add 1–2 tablespoons of oats; if too dry, drizzle 1 tsp honey at a time until it binds.
Scoop heaping tablespoons of the mixture and roll into 1-inch balls between your palms. Place each ball on the prepared sheet. You should make about 16 balls.
Chill the tray in the refrigerator for at least 20–30 minutes to firm up the balls. Chilling helps the peanut butter and honey set so they keep their shape.
Store finished protein balls in an airtight container in the fridge for up to 2 weeks, or freeze for longer storage. Let frozen balls sit at room temperature a few minutes before eating.