Heat sesame oil in a large skillet over medium heat. Add ground beef and cook until browned for about 6-7 minutes.

Add diced onion, minced garlic, and ginger to the beef and cook for 2 minutes until onion is translucent.

Stir in soy sauce, brown sugar, and gochujang. Simmer for 5 minutes until sauce thickens.

In a separate skillet, melt butter and toast the cut sides of the hamburger buns for 2-3 minutes until golden brown.

Assemble the sandwiches by spooning the beef mixture onto the toasted buns and adding desired toppings.