How to Make It
In a small bowl, whisk 1/4 cup of the apple cider vinegar with the beet juice, sugar and 1/2 teaspoon of salt until the sugar and salt are dissolved. Add the red onion and refrigerate for 1 hour. Drain before using.
In a small skillet, cook the bacon over moderate heat, stirring, until browned but still chewy, 5 minutes. Keep warm.
In a small bowl, whisk 1 tablespoon of the olive oil with 1 tablespoon of the bacon fat from the skillet and the remaining 1 tablespoon of vinegar. Season the vinaigrette with salt and pepper.
Light a grill. Rub the chard leaf with the remaining 1 1/2 teaspoons of olive oil and season with salt. Grill over high heat, turning, until lightly charred but still pliable, 3 minutes. Transfer to a work surface and let cool slightly, then thinly slice. Leave the grill on.
On a rimmed baking sheet or platter, spread an even layer of salt. Grill the oysters flat side up over high heat until the shells open slightly, 5 minutes. Using tongs, transfer the oysters to the prepared baking sheet, being careful not to spill the juices. Using a kitchen towel or mitt, remove the top shells. Spoon the vinaigrette over the oysters. Top with the chard, bacon and pickled onion; serve right away.