Prep Tomatoes: Slice the tops off the tomatoes and keep to one side. Carefully slice out the centre of the tomato, making sure to keep the outside intact. Scoop tomato into a mixing bowl and pat the insides of the tomatoes dry. Blitz the tomato filling with a hand blender until smooth. Place to one side.
Sausage: In a large pan over medium heat add a drizzle of olive oil with the diced onion. Fry until it begins to soften & pick up colour, then add garlic and fry for a couple of minutes longer. Add in sausage meat and break up with a wooden spoon. Continue frying/breaking up until browned and cooked right through. Stir in tomato paste and fry for 1-2mins.
Rice: Pour in the blended tomato, then add in rice, parsley, salt, pepper and chilli flakes. Give everything a stir, then reduce to a simmer and gently stir every now and then until the rice is just about cooked (still a teeny bit hard). Gradually add in stock as needed until the rice reaches this point. I typically end up using around 1/2cup/120ml, but just use as much as you need to get the rice al dente (use water if you run out of stock).
Stuff Tomatoes: Add in a dollop of the sausage & rice, then a pinch of mozzarella, then finish with another dollop of sausage & rice. Gently push down and level off, then add the top of the tomato back on.
Bake: Add to a baking dish and pop in the oven at 180C/350F for 20-30mins, or until the tomato is tender, but still firm enough to stay intact. Keep an eye on them, if they start to crack then reduce the heat slightly, or if they're tender enough just remove them from the oven.
Cheese: Take the tops off the tomatoes then sprinkle with mozzarella and parmesan. Pop under the grill and broil until the cheese is golden.
Serve: Add a dollop of pesto and a sprinkling of any leftover parsley you might have, then carefully remove from the dish and serve up!