1. Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy cleanup.
2. In a skillet over medium heat, add the olive oil and sauté the chopped onion until translucent, about 3-4 minutes.
3. Add the garlic and ground beef to the skillet, breaking the beef apart with a wooden spoon. Season with salt and pepper. Cook until the beef is browned and cooked through, about 6-8 minutes.
4. While the beef cooks, carefully slice the Hawaiian rolls in half horizontally, keeping them connected. Place the bottom halves on the prepared baking sheet.
5. Spread the mayonnaise and Dijon mustard evenly over the bottom halves of the rolls.
6. Once the beef is cooked, spoon it evenly over the mayonnaise and mustard layer. Top with slices of cheese.
7. Place the top halves of the rolls over the cheese and brush with melted butter. Sprinkle sesame seeds on top if using.
8. Bake in the preheated oven for 10-15 minutes, or until the cheese is melted and the rolls are golden brown.
9. Remove from the oven and let cool for a few minutes before slicing into individual sliders.

These simple steps will guide you to a platter of irresistible sliders, each bite a reminder of how rewarding home-cooked meals can be.