Bring a large pot of salted water to a boil. Add the calamari rings and cook for 2-3 minutes until they turn opaque. Be careful not to overcook, as this can make them tough.
Drain the calamari and immediately transfer it to a bowl of ice water to stop the cooking process. Let it chill for about 5 minutes, then drain again and pat dry with paper towels.
In a large mixing bowl, whisk together the olive oil, lemon juice, lemon zest, minced garlic, red pepper flakes (if using), salt, and pepper.
Add the chilled calamari, cherry tomatoes, red onion, and parsley to the bowl. Toss gently to combine, ensuring the calamari is well coated with the dressing.
Cover the salad and refrigerate for at least 30 minutes to allow the flavors to meld. Serve chilled.