For the chive mayo: Mix together the mayonnaise, yogurt, chives, lemon juice, mustard, 1/4 teaspoon salt and 1/4 teaspoon pepper in a small bowl; set aside. (The mayo can be made a day ahead and refrigerated.)
For the BLT salad bites: Saute the pancetta in a skillet over medium-high heat until crispy, 5 to 7 minutes. Transfer to a plate.
Combine the tomatoes, olive oil, chives, vinegar, 1/2 teaspoon salt and 1/4 teaspoon pepper in a medium bowl. Let sit for 5 minutes.
Arrange the larger lettuce leaves on a serving platter. Spoon about 1 1/2 teaspoons of chive mayo onto the center of each leaf. Top with about 1 tablespoon of the tomato mixture and some crispy pancetta. Sprinkle with the Parmesan.