Carefully scoop out the insides of the mushrooms caps. Drizzle with oil and rub in on both sides. Place bottom-up on pan. Bake for 10 minutes, then broil for 2 minutes.
In the meantime, heat the oil in a large pan on medium heat. Add the onion and garlic, stirring occasionally for 3-4 minutes, or until fragrant.
Add the pepper and continue cooking for 5 minutes, until softened.
Add the chicken and make sure to break it up while stirring. It should take 5-7 minutes until the chicken is cooked.
Put in the tomato paste and spices, mixing to coat everything evenly. Cook for 3-4 minutes, then mix in the olives.
Divide evenly between the mushroom caps.* Serve warm. Store in a container in the fridge.
Notes
*Depending on the size of your mushrooms, you may have extra chicken.
Recipe by Lenses and Lentils at https://lensesandlentils.com/mediterranean-stuffed-portobello-mushrooms/