In a large bowl, pour 1 cup boiling water over the bulgur. Cover with plastic wrap; let stand until water is absorbed, about 30 minutes.
Add cucumber, onion, parsley, garlic, lemon juice, oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper; toss to combine. Serve warm, cold, or at room temperature. (To chill, cool, then refrigerate in an airtight container for up to 1 day.)