Chopped Salad with Shrimp and Lime-Buttermilk Dressing

In a blender, combine buttermilk, avocado, lime zest and juice, and 2 tablespoons water. Blend until smooth, 20 seconds. Season dressing to taste with salt and pepper. In a large skillet, heat oil over medium-high. Season shrimp with salt and pepper. Cook until opaque throughout, about 3 minutes, flipping once. In a large bowl, toss together romaine, pepitas, cilantro, shrimp, and 1 cup dressing until combined and serve immediately.