How to Make It
Heat the olive oil in a deep 12-inch skillet. Add the sliced scallions and cook over high heat for 1 minute, until barely softened. Add the spinach and arugula and cook, stirring, just until wilted, about 2 minutes. Add the rice and cook, stirring, until it's coated with the olive oil and the grains begin to turn a milky-white color, about 3 minutes.
Stir 3 1/2 cups of the broth into the rice. Add the tomatoes, paprika, saffron, water, 1 tablespoon of kosher salt and 1/2 teaspoon freshly ground pepper; bring to a boil. Cook the Bomba rice, tomatoes and greens over moderately high heat, stirring occasionally, until some of the chicken broth has been absorbed, about 5 minutes. Add the remaining 3 1/2 cups of broth and cook over moderately high heat, without stirring at all, until the level of liquid is just under the surface of the rice, about 8 minutes.
Working quickly, arrange the shrimp and mussels on top of the rice, tucking them slightly under the surface. Continue cooking over moderate heat just until the shrimp curl and turn pink, the mussel shells open and the rice is tender and starting to sizzle and form a crust on the bottom of the skillet, about 10 minutes longer. Serve the paella at once.