Combine the maple syrup, soy sauce, liquid smoke, and peanut butter in a medium-sized bowl. Whisk vigorously until the mixture is consistent. Use an electric mixer or immersion blender as needed.
Add the mushrooms into a large bowl and add the mixed sauce. Toss so that the mushrooms are coated with sauce. Let marinate for 10 minutes, stirring occasionally, up to 30 minutes.
Heat the olive oil in a large skillet over medium-low heat until hot. Spread the mushrooms evenly in the skillet. It's OK if they overlap. Drizzle some extra marinade onto the mushrooms.
Allow the mushrooms to cook undisturbed until well browned on the bottom, about 5 minutes. Stir the mushrooms around to scrape up any hardening bits of sauce stuck to the skillet. Flip each mushroom slice over to let the other side cook until well-browned, about 5 minutes.
Taste a mushroom slice at this point. If you like the consistency (it will be firm but not crispy at this point) you may serve the mushrooms.
Continue to flip the mushrooms every 2-3 minutes to prevent scorching, until they reach the desired crispiness. You can also add marinade as needed, though it will slow the crisping process.
Serve hot.