Mix all the ingredients for the chipotle bbq sauce in a saucer and put over medium heat until reduced. About 20-25 minutes.
On a hot non-stick or cast iron skillet add the 3 tablespoons, make sure it covers the whole surface of the pan. Add the mushrooms and let them brown.
When the mushrooms have at least one browned side, add the sliced garlic and a pinch of salt. Let the mushrooms brown all around.
Slowly add the chipotle bbq sauce to the pan with the browned mushrooms. Let the mushrooms absorb the sauce a bit, the sauce will continue to thicken.
Prepare the slaw by mixing the mayo, the chipotle powder, salt, and vinegar first. Add the sliced red cabbage and mix. Test for seasoning and adjust if necessary.
Cut the pretzel sliders by half and toast them for a bit.
Divide the oyster mushroom mix between the four pretzel sliders, add more chipotle bbq sauce on top. Top the mushroom mix with the red cabbage slaw, some pickles and cilantro leaves. Place the top part of the pretzel slider ontop.
Notes
If you have leftover sauce, keep it in the fridge in a tightly closed jar for future uses.