For the tortillas, either wrap in a paper towel and prepare to microwave for about 45 seconds just before serving, or wrap in foil and warm in a 300-degree oven for about 10 minutes, just before assembly. Line a large plate with a double layer of paper towels for draining the avocados.
In a medium bowl, toss the cabbage, black beans, tomatoes, green onion and jalapeño with the lime juice and 1/2 teaspoon salt. Reserve.
In a small bowl or a squirt bottle, combine the sour cream and milk, and stir or shake to mix, reserve.
In another medium bowl, whisk the egg. Put the cornmeal, sesame seeds and paprika in another bowl.
Pour canola oil to a depth of about 1/2 inch into a large skillet and place over medium heat. Working quickly, slice each avocado in half, remove the pit, and then use the tip of your paring knife to slice each half in four slices lengthwise inside the shell. Use a spoon to scoop the slices out of the shell without breaking. Drop the slices into the egg and gently toss to coat. Coat each avocado slice in the cornmeal mixture, then carefully place in the hot oil. Once all the slices are in the pan, and the oil has returned to a sizzle, reduce the heat to medium-low.
