Combine soy milk and apple cider vinegar in a bowl. Stir until mixed and let sit for a few minutes.

In another bowl, mix all-purpose flour, garlic powder, onion powder, smoked paprika, and salt.

Dip the king oyster mushrooms in the buttermilk mixture, ensuring they are well coated.

Coat the mushrooms in the flour mixture, shaking off any excess flour to ensure even coverage.

Roll the coated mushrooms in panko breadcrumbs, gently pressing to adhere.

Heat olive oil in a frying pan over medium heat. Fry the mushrooms for about 25 minutes until golden brown and crispy, turning occasionally.