1. Chop 1/2 head romaine lettuce into 1/2-inch strips; place in bowl with 2 cups corn kernels and 1 cup tomatoes cut into bite-sized pieces.
2. Peel, pit, and cut 1 avocado into cubes; add 3/4 of cubes to bowl. In blender, puree rest with 1/3 cup water, 1 to 2 tablespoons fresh lime juice, and 1/4 teaspoon chili powder, season with coarse salt and ground pepper.
3. Pour over salad and toss gently.