Combine the cornmeal, flour, breadcrumbs, salt, cayenne and paprika in a pie plate. In another pie plate, whisk together the egg and buttermilk. Add the oysters to the egg-buttermilk mixture and turn gently with a large spoon to coat. Remove the oysters, one by one from the egg mixture with a pair of tongs and place in the crumbs. Turn several times to coat evenly with the crumb mixture, then transfer to a plate and let stand for 10 minutes.
While the oysters "rest," make the garlic-onion slaw. Place the cabbage and sliced onion in a large bowl and season with salt and pepper. In a separate bowl, whisk together the buttermilk, mayonnaise, garlic, sugar and hot sauce. Add to the cabbage-onion mixture and toss to combine. Taste and adjust the seasoning as needed. Set aside until ready to assemble the sandwiches.
Heat 1/4-inch of oil in a large skillet to 350°F (medium-high). Best if using enough oil in the pan to be equal to about 1/2 the thickness of the oysters. Test the temperature of the oil by adding a pinch of the dry crumb mixture - if it sizzles immediately, the oil is ready. Add 1/2 the oysters and fry until golden brown and crispy, turning once, about 2-1/2 minutes per side. Transfer to a paper towel-lined plate and blot very gently. Repeat with the remaining oysters.