Heat oil in a large stock pot over medium-high heat. Add onion, carrot, celery and garlic and season with salt and freshly ground black pepper. Cook, stirring occasionally, until tender. Add tomato paste and stir until it has melted in with the vegetables, about 1 minute.
Break tomatoes into small pieces with your fingers and add them to the pot along with their juice. Add zest, chili flakes, fennel, bay leaf, saffron, and vegetable broth to the pot and stir to combine. Bring to a boil, then lower heat to a slow simmer. Cook, uncovered, stirring and breaking up tomatoes with a spoon occasionally, for 20 minutes.
Add sugar, rice, and dill and cook until rice is tender, about 15 minutes more. Taste and season with more sugar, salt, and pepper as necessary. Serve.