Heat the oil in a large saucepan over medium heat. Add the onion; cook, stirring constantly, for 3 minutes. Add the garlic, thyme, fennel seed, salt, black pepper, and saffron; cook for 20 seconds.
Stir in the tomatoes, broth, and green beans. Bring to a simmer. Cover, reduce the heat and simmer for 2 minutes.
Increase the heat to medium, stir in the scallops, and cook, stirring occasionally, for 2 minutes. Add the shrimp and cook, stirring occasionally, for 2 minutes more.
