In a small nonstick skillet, add the ground beef. Heat the ground beef over medium-high heat and brown the meat until thoroughly cooked. Add ½ tsp kosher salt to the beef and stir well. Use a slotted spoon to remove the meat to a separate bowl. Leave the residual fat at the bottom of the pan.
Add the sliced mushrooms and add ⅛ tsp kosher salt. Cook for 2 minutes or so, stirring constantly until the mushrooms are browned.
Prep all the ingredients by dicing the onions and green bell peppers. Have the other ingredients ready to go into the bowls.
Then divide the ground beef between the four 2 cup sized stainless steel bowls (or other ovenproof bowls). Divide the mushrooms between the bowls on top of the beef. Add 1 tbsp each of diced bell pepper and white onion to each bowl.
Top each bowl with 2 tbsp pizza sauce to each bowl (be sure to find a no sugar added kind).
Top each bowl with ¼ cup of shredded mozzarella cheese, 1 tbsp black olives, and five pepperoni slices.
Set an air fryer to 400 F and place one bowl inside 4 minutes. Add more time for more browning.