In a large bowl mix peanut butter, protein powder, flax, salt, maple syrup, milk and vanilla. Stir well until combined.
Add oats, M&Ms and chocolate chips and mix until evenly combined.
Scoop mixture into 18 balls (using ~2 tbsp cookie scoop) onto the parchment-lined baking sheet. Roll each ball lightly with clean hands to shape. Note: if mixture is too dry, add 1 extra tbsp of milk or water at a time until easy to shape. If too wet, add 1 extra tbsp of quick oats at a time until easy to shape.
Enjoy right away or refrigerate until you’re ready to eat. Store in the fridge. Note: They're softer when they're first made, so if you prefer a firmer ball, chill them in the fridge for an hour or two first!