Turn on the vent hood because the cabbage will smoke and you want to start venting air out before continuing.
Trim just enough of the stem to remove the dark dirty part. Remove any damaged or discolored outer leaves.
Slice the cabbage in half leaving the core attached so it doesn’t fall apart. Slice each half into six pieces leaving the core intact.
Heat a cast iron pan over medium high heat and add 1 tablespoon oil. Place cabbage cut side down and sear until dark and charred - about 5 - 7 minutes depending on your heat. Check if blackened. Flip over and char other side. Repeat for remaining wedges.
Remove charred cabbage and set on a baking sheet or cutting board until cool enough to handle.
In a large bowl, whisk together the dressing ingredients.
Slice off core from the cabbage wedges and discard. Transfer cabbage along with red onions and any of the optional add-ins into a large bowl and toss with dressing.
If you would like to char the cabbage on the grill, I recommend slicing each half of the cabbage into 4 rather than 6 wedges. It's important to keep the core intact. Char each side of the wedge until nice and black. Slice off the core and cut into thinner strips and continue with recipe.