Heat the oven to 450°F. Bring a medium saucepan of water to a boil and salt it. Put the tomatoes in a medium bowl, sprinkle with salt and pepper, and drizzle them with 1 tablespoon olive oil; toss gently to coat.
When the water boils, stir in the rice and adjust the heat so that the water bubbles steadily. Cook, stirring once or twice, for 12 minutes, then drain thoroughly.
Put the remaining 3 tablespoons oil in a large skillet over medium-high heat. Add the onion and garlic, sprinkle with salt and pepper, and cook, stirring occasionally, until the onion softens, 3 to 5 minutes. Transfer to a bowl with a slotted spoon. Add the green beans, bell pepper, and eggplant to the skillet, sprinkle with salt and pepper, and cook, stirring once in a while, until browned in spots but still crisp, 5 to 10 minutes; add more oil if the mixture looks too dry. Transfer to the bowl and toss to combine; taste and adjust the seasoning.
Add the rice to the pan and stir until shiny and toasted, about 1 minute. Add the tomato paste, paprika, and saffron and stir until fragrant, about 1 minute more. Add 2 cups stock; stir gently to combine. The rice should be submerged by ½ inch; if not, add a little more liquid.
Scatter the browned vegetables on top, followed by the tomatoes; drizzle with any accumulated juices. Put the pan in the oven and cook, undisturbed, for 15 minutes. Check to see if the rice is dry and just tender. If not, return the pan to the oven for another 5 minutes. If the rice looks too dry at this point, but still isn’t quite done, add a small amount of stock or water. When the rice is ready, turn off the oven and let it sit for at least 5 and up to 15 minutes. Garnish with the parsley and serve.