Cut the bell peppers in half and and remove the seeds. Place on a foil lined baking sheet.
Heat the oil on a medium high heat in a skillet on the stovetop, add the onions and cook til soft.
Stir in the minced garlic and cook for a minute or two.
Add in the ground chicken and cook til browned.
Add in the marinara sauce and grated parmesan. Stir to combine and take off the heat.
Spoon the chicken mixture into the pepper halves and top with the breadcrumbs.
Bake in the oven for 20 minutes.
Remove the peppers, top each with the mozzarella and broil for a few minutes until the cheese melts.
Notes
Choose bell peppers that are quite round in shape, so you can fill them more easily.
Remove the seeds and the ribs of the peppers before stuffing them. The easiest way to do this is with a teaspoon.
I prefer to cut the peppers in half lengthways as they cook quicker and are easier to eat. You can cut the tops off of the peppers and fill them whole if you prefer.
If you have any leftover chicken parmesan mixture, keep it covered in the fridge for up to 4 days. You can reheat it and stir it into pasta.