Preheat the oven to 400F/200C. Chop the potatoes into small-ish wedges or dice. Toss the potatoes with around 1 tablespoon of olive oil in a baking dish large enough to hold the potatoes in one layer along with the tomatoes in between them. Once the oven has heated, add the dish with the potatoes so they start cooking as you par-cook the rice.
Warm another 1 tablespoon in a skillet/frying pan over a medium heat. Add the garlic and cook, stirring regularly, for a minute or two until it is fragrant but not browning. Add the rice and stir to coat with the oil and garlic. Cook a minute then add around ¾ cup (360ml) of the tomato pulp. Bring to a simmer, reduce the heat and cook, stirring now and then, for around 10 minutes.
Add the parsley, basil, oregano, salt and pepper. Mix through so well distributed and cook a minute or two longer. If needed, add a little more of the tomato pulp - it should seem slightly wet but not soup-y. Once the rice is just about cooked (so it seems about cooked but with a little bite), remove from the heat.
Remove the dish with the potatoes from the oven, and carefully add the tomatoes, open side up, between the potatoes so that you have potatoes all around and in between the tomatoes. Fill each tomato with the rice mixture, splitting it evenly between the tomatoes. Don't press the mixture down but leave it loose. You can add a drizzle more tomato pulp on top of the rice, but you won't need much, if any.
Add the tomato tops on top of each tomato - if they match up, great, but it's fine if they don't. Drizzle the remaining 1 tablespoon of olive oil over the top of the tomatoes then return the dish to the oven and allow to bake for around 40 - 50 minutes, until the rice has cooked through, the potatoes are gently brown and the tomatoes soft.