1. Line two 10-by-15-inch baking sheets with cooking parchment or silicone baking liners. In a bowl, with an electric mixer at medium-high speed, beat egg whites and salt just until stiff (but not dry) peaks form, 2 to 4 minutes. Reduce speed to medium and add sugar gradually, beating until it has dissolved and whites are glossy and like marshmallow creme in texture, about 3 minutes.
2. With a flexible spatula, gently fold in chocolate, pistachios, and orange peel.
3. Drop mixture in tablespoon portions about 1 inch apart on baking sheets. If desired, swirl the back of a spoon (or your finger) around cookies to shape.
4. Bake in a 250° regular or 225° convection oven until meringues appear set and are just beginning to turn pale gold at edges, about 50 minutes, switching baking sheet positions halfway through baking. Turn off oven and leave cookies inside on sheets until dry in the center (break one to test), at least 4 hours or up to 12. Store airtight at room temperature up to 2 weeks.
Nutritional analysis per cookie.