Combine the lobster, celery, mayonnaise, 1 tablespoon of the lemon juice, 1 teaspoon salt, and ½ teaspoon pepper in a medium bowl and set aside. Combine the avocados in another bowl with the remaining 1 ½ tablespoons of lemon juice, 1 ½ teaspoons salt, and ¾ teaspoon pepper and coarsely mash together with a fork. Place the bottom halves of the rolls on a board and spread with the avocado mixture. Arrange the lobster mixture on top. Replace the roll tops and serve at room temperature.
