Preheat the oven to 350°F. . Lightly spray a 13 x 9-inch baking dish with cooking spray. Set aside.
In a medium skillet over medium-high heat, cook the diced onion in a couple of drizzles of olive oil until translucent.
Add the ground beef to the pan. Season with garlic salt and black pepper. Cook until no pink remains, then drain any excess fat from the pan.
Add the chili powder, cumin, mustard, cayenne, ketchup and Worcestershire sauce to the pan. Simmer for 10 minutes then remove from the heat. (This can be made in advance and chilled until assembly)
Arrange the buns in the baking dish and brush on all sides with melted butter. Place one hot dog in each bun and top with a drizzle of mustard and ketchup.
Divide the chili sauce among the hot dogs and top each with cheese.
Cover with a piece of aluminum foil spritzed with cooking spray.
Bake for 30 minutes. Uncover in the last 5 minutes continuing to bake until the tops are lightly toasted.
Garnish with sliced green onion and serve with sweet pickle relish and cole slaw on the side, if desired.