Heat oven to 350°F. Line a rimmed baking sheet with parchment paper, and set aside. Spread walnuts on a separate rimmed baking sheet, and toast in oven for 7 to 10 minutes. Remove from oven and let cool.

Combine cardamom, ginger, cinnamon, and salt in a small mixing bowl, and set aside.

In a medium saucepan, heat sugar and water over medium-high heat, and cook without stirring until syrup dissolves and turns a deep amber color, 7 to 10 minutes.

Quickly add spice mix and the walnuts to the saucepan, and stir to combine. Spread nuts onto lined baking sheet, and return to oven. Bake for another 7 to 10 minutes. About halfway through baking, open oven, use a fork to break any nut clusters apart, and sprinkle nuts with additional salt, if you like.

Remove from oven. While nuts are still hot, break up any remaining clusters with a fork. Cool completely. Stored in an airtight container, nuts will keep at room temperature for about a week.