Brush your mushroom caps with olive oil, and sprinkle with salt and pepper. Place in the air fryer for 10 minutes. Remove and set aside, keeping them warm.
Place the sliced peppers and onions in an air fryer. Set to 350 degrees F and cook for 10 minutes, until vegetables are tender and cooked through.
Slice the brats, and add to the Air fryer. Cook the brats and vegetables for 5 minutes, until the brats are warm throughout.
Place the mushroom caps upside down on a serving plate. Put the vegetables and brat mix on top of the mushrooms and enjoy!