How to Make It
In a large bowl, whisk the salt with 6 cups of cold water until dissolved. Add the chicken and refrigerate for 45 minutes. Remove the chicken and pat dry with paper towels. Wipe out the bowl.
In the same bowl, whisk the olive oil with the garlic, rosemary, lemon zest and crushed red pepper. Add the chicken and turn to coat, rubbing some of the marinade under the skin. Marinate the chicken at room temperature for 45 minutes.
Light a grill or preheat a grill pan. Grill the chicken over moderate heat, turning occasionally, until lightly charred and an instant-read thermometer inserted in the thickest part of each leg registers 165°, about 25 minutes.
In a large cast-iron skillet, cook the scallions over high heat until charred on the bottom, about 3 minutes. Transfer to a work surface and cut into 1-inch lengths. In the same skillet, heat the olive oil. Add the onion and a generous pinch of salt and cook over moderately high heat, stirring occasionally, until softened and lightly browned, about 6 minutes. Add the sausage and cook, breaking up the meat with a wooden spoon, until nearly cooked through, 6 to 8 minutes. Add the corn and tomatoes and cook, stirring occasionally, until the corn is crisp-tender and the tomatoes are softened, about 5 minutes. Stir in the snap peas and cook until crisp-tender, about 2 minutes longer. Stir in the basil and scallions and season with salt. Transfer the fricassee to a platter, top with the chicken and serve.