In a large bowl, mix together ground beef, chopped onion, an egg, and seasoning (salt, black pepper, and red pepper flakes).
Using a 3 tbsp scoop, scoop the mixture and form into oval patties. Dip them into dry bread crumbs, so they are covered with it from all the sides.
Preheat a large skillet on a medium heat, add a tablespoon of vegetable oil and a tablespoon of butter. Depending on diameter of your skillet, you might want to add one extra tablespoon of oil. Sauté the cutlets for about 5 minutes on each side, covered with a top lid.
To make sure they are cooked inside, just cut one of the cutlets with a knife. It should be still juicy but without blood.