Preheat oven to 400 degrees F (204 C) and line a baking sheet with parchment paper and set an oven-safe baking/cooling rack on top for crispiness (if you don’t have a cooling / baking rack, just omit — it helps the “bacon” get crispier but isn't necessary).
Prepare marinade by adding avocado oil, maple syrup, apple cider vinegar, coconut aminos, paprika, salt, liquid smoke, miso paste, and black pepper to a medium mixing bowl and whisking to combine. Taste and adjust flavor as needed, adding more liquid smoke or paprika for smokiness, pepper for spice, vinegar for acidity, maple syrup for sweetness, or salt to taste.
Once the marinade is seasoned to your liking, add the sliced mushrooms to the bowl and gently toss / stir to coat. I prefer using my hands to toss the mushrooms in order to handle them more carefully and coat them more thoroughly.
Lay mushrooms on the oven-safe baking/cooling rack set over the parchment-lined baking sheet (or just directly on the parchment paper) and spread into an even layer, making sure the mushrooms are touching as little as possible.
Bake for 15-25 minutes in the top third of the oven, or until darker golden brown in color and fragrant. How long you bake the mushrooms depends on how crispy you like your mushroom “bacon.” Check at the 15-minute mark and every 5 minutes thereafter to check for doneness.
Remove from oven, peel off of cooling rack, and enjoy immediately with your favorite breakfast items, such as roasted sweet potatoes or in a scramble. Would also be delicious in vegan/vegetarian BLT sandwiches, wraps, or salads!
Store leftovers covered in the refrigerator up to 3-4 days and reheat in the microwave or on the stovetop until warm. Not freezer friendly.