Combine crab with 3/4 cup of the sour cream.
Spoon 2 rounded tablespoons of crab mixture across lower third of each crepe and roll to enclose.
Place filled crepes, seam side down, in a lightly greased 9 by 13-inch baking pan.
Evenly sprinkle with cheese.
Cover and bake in a 400° oven for 20 minutes.
While crepes are baking, peel, pit, and slice avocados; coat slices with lemon juice.
To serve, spoon some of the remaining 1/2 cup sour cream over each crepe and top with several slices of avocado.