Prep: 1. Juice and zest the limes (you should get about 1/4 cup juice and 1 teaspoon zest). 2. Slice avocado. 2. Mix in blender: buttermilk, avocado, lime zest and juice, and 2 tablespoons water. Season with salt and pepper. Make: 1. In a large bowl, toss together romaine, pepitas, cilantro, shrimp, and dressing to taste; serve immediately.