Place mushroom slices in a resealable plastic bag. Whisk soy sauce, chili paste, rice vinegar, and sesame oil together in a bowl until completely blended. Pour over mushrooms, seal the bag, and refrigerate for 8 hours.

Preheat the oven to 250 degrees F (120 degrees C). Line a baking sheet with parchment paper. Arrange mushroom slices on the baking sheet in such a way that they are not touching each other.

Bake in the preheated oven for 1 hour. Flip mushroom slices using tongs and cook for 1 more hour. Remove baking sheet from the oven and let cool completely before storing. For any larger slices that are not dry after 2 hours, crack open the oven door and let cook 5 additional minutes or until dry.