To prepare tempeh, combine first 6 ingredients in a large nonstick skillet; add tempeh, tossing lightly to coat. Bring to a boil. Cover, reduce heat to low, and simmer 15 minutes.
Uncover mixture and increase heat to medium-high. Cook 4 minutes or until golden brown, turning frequently. Cool.
To prepare sauce, heat a small saucepan coated with cooking spray over medium-high heat. Add onion, 2 teaspoons ginger, salt, and 2 garlic cloves; sauté 5 minutes. Stir in curry powder and turmeric; sauté 1 minute. Add water. Bring to a boil, and cook 1 minute. Cool 5 minutes.
Pour onion mixture into a blender, and add cashews and lemon juice. Process until smooth. Place a toothpick in each tempeh cube. Serve with warm cashew sauce.