Add the vegetable oil or a cast iron skillet, Dutch oven, or other heavy, shallow pan. Heat the oil over medium heat until completely hot.
While the oil is heating, add the cornmeal, flour, and salt to a bowl. Mix to combine.
Make a well and add the egg and buttermilk. Whisk the egg and buttermilk together to thoroughly break up the egg, then begin whisking the cornmeal mixture into the egg mixture. Thoroughly combine, with small lumps being okay.
Fold in the okra. It can be fresh or frozen, and if it is frozen, you do not need to defrost it first.
Fold in the onions.
Once the oil is hot, carefully spoon batter into the skillet until each one is about 3" across. You can make them larger or smaller to your preference, but this may affect cooking time.
Fry on the first side for about 2-3 minutes or until the bottom is golden brown and crusty.
Flip carefully and fry on the second side for an additional 2-3 minutes or until that side is brown and crusty.
Remove the fritter to a paper-towel lined plate or a cookie rack set over a baking sheet. Allow the fritters to cool and to drain off any excess oil.
Serve warm and enjoy!