Crush hazelnuts into flour using a coffee grinder and set aside. (To crush the hazelnuts you can also use a mortar and pestle, or blender, but the coffee grinder will work best in this case due to the small amount of nuts needed, plus their size and texture.)
Add white wine vinegar, lemon juice, and honey to a small pot or stove-safe measuring cup over low heat.
Stir until honey dissolves and becomes liquid.
Add the crushed hazelnuts, and stir until smooth.
Remove from heat, and add olive oil (if being used) and water.
Cool before enjoying.
For the Salad
Combine arugula, chopped grapes, chopped blood orange, halved hazelnuts, and crumbled goat cheese to a bowl.