Heat oven to 350°F.
Line 2 baking sheets with parchment or waxed paper. With mixer, beat egg whites until frothy. Add powdered sugar, cocoa powder, flour, ground coffee, if using, and water. Beat on low to combine; on high, beat until thick like marshmallow topping, 3 minutes.
Fold in pecans. Drop by heaping teaspoonfuls onto sheets. Bake at 350°F for 10 minutes, until tops crack. Cool on sheet on rack.