Place lettuce in a large bowl. Layer peas, bell pepper, tomatoes, celery, and scallions on top.
Whisk yogurt, mayonnaise, vinegar, sugar to taste, garlic powder, salt, and pepper in a medium bowl until smooth. Spread the dressing evenly over the top of the salad (an offset spatula is handy for this, if you have one). Sprinkle with cheese, basil, and bacon. Serve room temperature or chilled.