In a large bowl combine mayonnaise, sour cream, scallions and lemon juice. Add ham, celery, peas, water chestnuts, almonds, pimentos and pepper. Spoon into prepared baking dish. Top with cheddar cheese.
1/2 cup mayonnaise, 1/2 cup sour cream, 2 tbsps scallions, white and green part, more for garnish, 2 tbsps fresh lemon juice, 3 cups cubed ham -1/2" pieces *, 1 cup chopped celery, 1/2 cup frozen peas, thawed, 8 oz sliced water chestnuts, drained, 1/2 cup slivered almonds, 2 tbsps chopped pimentos, 1 tsp coarsely ground black pepper, 1-1/2 cups extra sharp cheddar cheese