Remove leaves and core from cauliflower and break into florets. Place florets in a food processor and pulse about 10 times, until pieces have broken down and resemble rice or couscous.
Add parsley and mint and pulse again until uniformly mixed with the cauliflower.
In a large bowl, whisk together lemon juice, olive oil, red wine vinegar, garlic, and salt.
Transfer cauliflower mixture to the bowl, and add tomatoes, cucumber, and onion. Stir well to mix with the dressing.
Serve immediately or chill in the refrigerator until ready to serve.