Peel your onions and slice them into long, thin strips. Dice the red bell pepper into small pieces.
Stuff the onion and red bell pepper into clean glass mason jars. Push them down gently to fit as many as possible.
In a small saucepan, combine the vinegar, water, sugar, salt, and turmeric. Heat it on the stove just until the sugar and salt have completely melted, then remove from the heat.
Pour the warm brine over the onions in your jar until they are fully covered. Put a lid on the jar and let it cool on the counter. Place it in the refrigerator for at least 24 hours so the flavors soak in.