Preheat oven to 180 degrees C. Line a 20x30cm baking dish with aluminium foil.
In a large bowl, mix together beef mince, breadcrumbs, Italian seasoning, garlic, 1/2 cup (60g) of the mozzarella cheese, 1/2 cup (60g) of the Parmesan cheese, egg, onion and mushrooms. Spoon mixture evenly into the seeded capsicums. Replace tops. Place stuffed capsicums in lined baking dish.
Bake in preheated oven for one hour or until meat stuffing is cooked through. Remove from oven and discard capsicum tops.
Sprinkle tops of peppers with remaining mozzarella and Parmesan cheeses. Return dish to oven until cheese is melted, about 2 minutes.
In a saucepan, heat pasta sauce on stove over medium heat, stirring regularly. When sauce begins to steam, remove from heat and pour over top of capsicums.