Slice bell peppers into thin strips and banana peppers into thin rings and pack them all into a quart-sized mason jar.
Roughly chop garlic cloves and add them to the jar with the peppers. Try to pack them down a little.
Add vinegar, water, sugar, salt, MSG, and red pepper flakes to a small saucepan over medium-high heat.
Bring the vinegar mixture to a boil. As soon as it starts boiling, stir the mixture, remove from the heat, and pour it into the jar over the peppers. This is obviously a hot pot pouring hot liquid so be careful. I typically do the pouring process in the sink so any spilled near-boiling liquid does not hurt anyone.
Close the jar lid and let rest on your counter until cool.
Add to the fridge and enjoy some great pickled peppers on sandwiches over the next few weeks.