To prepare tempeh, heat a medium saucepan over medium-high heat. Add first 5 ingredients to pan, stirring with a whisk. Add tempeh; bring to a boil. Cook 3 minutes or until liquid is almost evaporated, stirring frequently. Place tempeh mixture in a medium bowl; cover and keep warm.
To prepare sauce, heat oil in a small saucepan over medium-high heat. Add cashews to pan; cook 2 minutes or until lightly browned. Add onion to pan; sauté 3 minutes or until tender. Add curry powder and 1 garlic clove to pan; cook 1 minute, stirring constantly. Remove from heat. Stir in milk.
Place cashew mixture, 2 tablespoons hot water, and salt in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth, scraping sides. Add cashew sauce to tempeh in bowl; toss gently to coat. Serve with pita wedges.