Butter-Lettuce Salad with Avocado-Buttermilk Dressing

Combine avocado, garlic, dill, lemon juice, buttermilk, and 2 tablespoons water in a blender; puree until smooth. Season with salt and pepper. (If dressing is too thick, add more water, a tablespoon at a time.)

Toss together lettuce, cucumber, bacon, and radishes in a large bowl; season with salt and pepper. Drizzle with 1/4 cup dressing. Serve remaining dressing on the side, or refrigerate in an airtight container up to 2 days.