Preheat your oven to 250°F (120°C) and line a baking sheet with parchment paper.
In a mixing bowl, combine soy sauce, maple syrup, smoked paprika, garlic powder, onion powder, and black pepper.
Add the sliced Portobello mushrooms to the bowl and toss to coat them evenly with the marinade.
Arrange the mushroom slices in a single layer on the prepared baking sheet.
Bake in the preheated oven for about 60 minutes, flipping the slices halfway through, until they are dry and chewy.
Let the jerky cool completely before storing in an airtight container.