Cook cumin and celery seeds in a hot nonstick skillet over medium-high heat, stirring constantly, 2 minutes or until seeds are toasted.
Place seeds in a large bowl; whisk in mayonnaise and next 3 ingredients.
Halve cucumber lengthwise; seed and cut into 3/4-inch-thick slices. Place cucumber and cabbage in bowl with dressing; toss to coat. Cover and chill 4 hours. Garnish, if desired. Serve with a slotted spoon.