To prepare steak, place steak in a large shallow dish. Drizzle with 2 tablespoons juice, and sprinkle with 1/2 teaspoon pepper; rub into steak. Cover; let steak stand at room temperature for 20 minutes, turning occasionally.
Remove steak from dish; discard marinade. Sprinkle steak with 1/4 teaspoon salt. Place steak on a grill rack coated with cooking spray; grill 8 minutes on each side or until desired degree of doneness. Let stand 10 minutes before thinly slicing.
To prepare salad, combine cucumber, tomatoes, lettuce, avocado, and onion in a large bowl. Combine cilantro and the remaining ingredients. Drizzle cilantro mixture over cucumber mixture; toss gently. Serve with steak.