Make vinaigrette: Combine olives and the water in the bowl of a food processor fitted with the metal blade. Process until olives are finely chopped. Add garlic, basil, vinegar, and cumin; process until mixture is smooth and combined, stopping to scrape sides of bowl with a rubber spatula as needed.
In a medium bowl, combine beans, tomatoes, and red onion, and gently toss. Pour vinaigrette over bean mixture, and toss well to coat. To serve, divide arugula leaves among four plates, and mound bean mixture on top.