Season the chicken with salt and pepper. Heat 1 Tbs. of the oil in a medium sauté pan over medium-high heat. Add the endive and cook, stirring frequently, until deep green but still crisp-tender, about 90 seconds. Transfer to a medium bowl.
Heat another 1 Tbs. oil in the pan and add the chicken. When the underside of the chicken has turned deep golden brown (after about 1 minute), turn it with a metal spatula. Turn occasionally for even browning until almost cooked through, 3 to 5 minutes, and transfer to the bowl of endive.
Reduce the heat to medium, heat the remaining 1 tsp. oil in the pan, and then add the garlic and crushed coriander. Cook until fragrant, about 30 seconds. Add the water or broth, orange juice, and vinegar. Use a wooden spoon to scrape up any browned bits in the pan and blend them into the sauce. Simmer vigorously until the sauce has reduced and thickened slightly, 2 to 3 minutes. Add the butter, stirring until blended. Stir in the chicken and endive along with any juices, season with salt and pepper to taste, and serve sprinkled with the parsley and walnuts.