In medium saucepan, mix Knox with 4 tablespoons Sugar, blend in egg yolks beaten with milk. Let stand 1 minute. Stir over low heat until gelatin is completely dissolved, about 5 minutes. With whip or rotary, blend in avocado and lemon juice. Pour into large bowl and chill, stirring occasionally, until mixture mounds slightly when dropped from a spoon. In medium bowl, beat egg whites until soft peaks form; gradually add remaining Sugar and beat till stiff. Fold into gelatin mixture. Turn into prepared crust. Chill until firm. Brush generously with additional lemon juice.