Add the olive oil to a large skillet over medium-high. Add the ground beef and cook, stirring, until all traces of pink are gone. Drain the ground beef and return it to the pan. Add the refried beans and stir until well mixed with the cooked beef. Add the taco seasoning mix, salt, and oregano. Mix well.
Place the beef and bean mixture into a baking dish that has been coated with cooking spray.
On top of the beef-bean layer, add the salsa, black olives, and green onions. Dollop on the sour cream and carefully spread it over the top. Finish with the cheddar cheese.