Place the avocado chunks in a small bowl and drizzle with lemon juice. Add ¾ teaspoon salt, and ¼ teaspoon black pepper. Toss gently to coat.
Place the chopped lettuce in the bottom of a salad bowl.
Top the lettuce evenly with the prepared mandarin orange segments and the prepared avocado chunks.
Cover and keep chilled for up to 4 hours (if needed).
In a medium bowl, whisk together the mayonnaise, orange zest, orange juice, and poppy seeds until smooth and creamy. Keep chilled until ready to serve.
Before serving, season the salad lightly with additional salt and pepper (if desired), and drizzle the dressing over the salad.