Combine cilantro, Greek yogurt, garlic and lime juice in the bowl of a food processor. With the motor running, add olive oil and vinegar in a slow stream until emulsified; set aside.
for the salad
To assemble the salad, place romaine lettuce in a large bowl; top with tomatoes, corn, black beans and cilantro. Pour the dressing on top of the salad and gently toss to combine. Stir in avocado.
Serve immediately, garnished with tortillas strips, if desired.