Southwest Spinach Salad

For the Dressing:

 cup plain Greek yogurt

 avocado, peeled and pitted

 tablespoons freshly squeezed lime juice

 cup fresh cilantro

 teaspoon kosher salt

water, plus more as needed

For the Salad:

baby spinach

can black beans, rinsed and drained

canned corn, drained

halved cherry tomatoes

 cup chopped red onion

 avocado, sliced