Preheat the oven to 375 degrees F (190 degrees C).

Bring chicken stock and bay leaves to a boil in a large saucepan. Reduce heat and simmer while preparing the other ingredients. Taste stock; it should taste a little over-salted. Season with 1 to 2 teaspoons salt and 1 teaspoon black pepper as needed.

Season chicken with salt and pepper.

Squeeze out seeds from each tomato half over a sieve and into a bowl. Reserve the juice and discard the seeds. Grate the cut sides of the tomatoes over a bowl through the large holes of a box grater. Discard the skin. Combine the tomato juice and the grated pulp.

Heat a large skillet over medium-high heat for 2 to 3 minutes and coat with 1 tablespoon olive oil. Add chicken in batches, in a single layer with space between pieces. Saute until meat is mostly opaque, about 4 minutes; it will continue cooking in the oven. Place chicken in a 9x13-inch baking pan. Repeat with the remaining chicken, being careful not to burn the fats rendering in the skillet.

Add 2 tablespoons olive oil to the same skillet. Add the tomato juice-pulp mixture. Cook, scraping up browned bits from the bottom of skillet, until juices are mostly evaporated, about 5 minutes. Add 2 teaspoons salt, 1 teaspoon black pepper, and paprika. Mix well. Add onions and garlic; saute until is fragrant, about 3 minutes. Stir the mixture, called a sofrito, into the baking pan with the chicken.

Heat the last tablespoon of olive oil in the hot skillet. Add green beans and saute for 1 minute. Add bell peppers; saute until green beans are crisp-tender, about 2 minutes more. Transfer mixture to the baking pan and stir well; mix in quinoa and saffron.

Remove and discard bay leaves from stock and bring to a boil. Pour 1/2 into the baking pan. Mix carefully until well combined. Add remaining stock and stir carefully. Lay rosemary sprigs on top.

Bake in the preheated oven until quinoa is tender yet firm to the bite, 35 to 45 minutes.