Heat oven to 350°F. Spray large cookie sheet with cooking spray. Separate dough into 8 biscuits; place 2 1/2 inches apart on cookie sheet. With bottom of flat 2-inch-diameter glass or with fingers, press biscuits into 3 1/2-inch rounds with 1/4-inch rim around outer edge.
In small bowl, beat egg yolk and water with fork until well blended. Brush over tops and sides of biscuits. Sprinkle each with sesame seed. Bake 13 to 17 minutes or until golden brown.
Meanwhile, in medium bowl, mix mayonnaise, cilantro, salt, pepper, Cajun seasoning and green chiles. Stir in tuna; set aside.
Set oven control to broil. Spoon about 1/4 cup tuna mixture into indentation in each biscuit; sprinkle each with 1/4 cup cheese. Broil 4 to 6 inches from heat 1 to 2 minutes or until cheese is melted. Carefully remove biscuits from cookie sheet. Garnish with tomato and lettuce.