Combine the chicken stock, fennel seeds, curry powder, saffron, red pepper flakes, 1 tablespoon salt, and 1 teaspoon black pepper in a large saucepan, bring to a simmer, remove from the heat, and set aside.
Heat the olive oil in a medium (10-inch) Dutch oven, such as Le Creuset, add the onion, and cook over medium heat for 5 minutes, until tender. Add the garlic and cook for one minute. Stir in the rice and cook for 2 minutes. Stir in the stock mixture, bring to a boil, lower the heat, and simmer covered for 10 minutes. Stir in the chicken, cover, and cook for 10 minutes. Stir in the shrimp, cover, and simmer for 5 minutes, until the shrimp are barely cooked and the rice is almost tender. Turn off the heat, cover, and allow to sit for 15 minutes.
Meanwhile, in a very large bowl, combine the celery, scallions, peas, red peppers, yellow peppers, kielbasa, and olives. Stir in the warm rice mixture and the lemon juice and set aside to cool. Boil 1/2 cup water in a medium saucepan, add the mussels, cover, and simmer for 4 to 5 minutes, until the mussels open. Add the mussels to the salad. Cover the salad and allow it to sit at room temperature for about an hour to allow the flavors to blend. Taste for seasonings and serve at room temperature.
Originally published as Summer Paella Salad in "Make it Ahead" by Ina Garten © Clarkson Potter 2014. Provided courtesy of Ina Garten.