For the slaw, whisk up dressing in a large bowl, add cabbage and toss to coat. Chill until ready to serve.
For the sauce, heat a skillet over medium heat, melt butter and add onions, garlic, salt and pepper. Soften 6-7 minutes then add chipotle purée and tomato paste. Stir a minute and add stock, Worcestershire, Tamari and sugar. Bring to a bubble then reduce to low simmer.
Heat a cast-iron griddle or skillet over medium to medium-high heat.
Make 4 patties that are thinner at the centers than edges for even cooking. Season patties liberally with salt and pepper.
Add a drizzle of oil to the griddle or skillet, and cook patties about 8 minutes, turning occasionally.
Arrange bun bottoms on a platter or plates and top with pickles and onions.
Turn burger patties in the barbecue sauce to coat then place on buns, top with slaw and set bun tops in place.
