Preheat the oven to 350°F (175°C) and grease a large rimmed baking sheet with butter.
Heat olive oil in a large skillet over medium-high heat and sauté finely diced onion until softened.
Add ground beef, break up with spatula, and season with salt, pepper, and garlic powder.
Cook beef thoroughly over medium-high heat, stirring frequently, until no pink remains.
Tilt skillet and carefully discard excess fat and liquid to prevent soggy sliders.
Remove skillet from heat and stir mayonnaise into the cooked beef mixture for moisture.
Slice the dinner rolls horizontally in half using a sharp knife.
Place bottom halves of rolls in a single layer on the prepared baking sheet.
Arrange sliced cheddar cheese evenly over the bottom buns.
Spread the seasoned ground beef mixture evenly over the cheese layer, squaring off edges.
Sprinkle shredded cheddar cheese evenly over the beef layer.
Place the top halves of the rolls cut-side down snugly over the assembled sliders.
Brush melted butter over the tops of the rolls and immediately sprinkle sesame seeds on top.
Bake uncovered for 12-15 minutes until cheese is melted and tops are golden and toasted.
Remove from oven and slice sliders into individual portions along roll lines; serve warm.