In a small bowl, combine the orange juice, the white vinegar, the salt, the dried oregano (rubbed finely with the heel of one hand into the palm of the other), and the black pepper.
Add the red onion and let steep.
Put your smallest sauté pan on the stove. Crank it to high. Let it get hot for about a minute. Now, turn it off.
Have a soup spoon handy, and then put the chile into the pan. Keep your face away. Even this small amount can take your breath away.
Let the chile wilt for 1 minute while stirring. You might get some char. That's good.
Spoon the chile into the vinegar mixture. Stir, and let macerate at room temperature for 15 minutes before serving.