Wash the mushrooms and pluck off their stems. Place the olive oil in a large bowl and swish the mushroom caps around in the olive oil.
Preheat the oven to 350°F. Line a 9x13" baking sheet with parchment paper and place each mushroom cap in the pan.
Heat a 10" cast iron skillet over medium to low heat with 1 teaspoon of fat in it. Place the sausage in the skillet and cook the sausage while breaking it apart with a spatula.
Once the sausage has been cooked and broken apart, add the onion, bell pepper, garlic, herbs, salt, and pepper. Add more fat if needed. Cook for 5-6 minutes, stirring occassionally.
Add the tapioca flour and stir it in well. The mixture will become sticky. Remove the skillet from the heat.
Take spoonfuls of the sausage mixture and start stacking the filling into the mushroom caps. Since the mixture is sticky you can stack it high!
Once all the mushroom caps have been filled, bake the mushrooms for 25-30 minutes.