Set out five 16-ounce mason jars. (I prefer the wide-mouth jars which are easier to fill.)
Make dressing by whisking together coconut milk, soy sauce, peanut butter, brown sugar, and red pepper flakes in a microwave-safe bowl. Microwave on high until peanut butter melts, about 30 seconds. Whisk in oil.
Divide dressing between jars.
Bring a pot of water to boil in the microwave or on the stovetop. Once the water is boiling, turn off the heat and then add ramen noodles (remember to discard the seasoning). Soak in hot water until tender, about 2 minutes. Drain.
Divide noodles between mason jars.
Top the noodles with bell peppers, carrots, chicken, and spinach (in that order).
Gently press the salad ingredients down and top with a lid.
Store mason jars in the fridge for up to five days.
Serve the salad by 1) transferring salad to a bowl and tossing everything together or 2) inverting the jar for a few minutes so that the dressing drips down over the other ingredients and then eating the salad straight out of the jar (this is how I prefer to eat my mason jar salads - everything won’t be totally mixed together, but it saves on dishes!).
Top the salad with peanuts right before serving.