Mini Cheeseburger Sliders


2 lb lean ground beef, (90/10 or 93/7 fat content)
1/2 Tbsp olive oil
1 tsp salt
1 tsp black pepper
1 tsp garlic powder
1/2 large yellow onion, finely diced
1/4 cup mayonnaise
8 slices medium cheddar cheese
6 oz medium cheddar, shredded (or used more sliced cheese)
24 dinner rolls, (or use 2 packs of 12)
2 Tbsp unsalted butter, melted, plus more to grease baking sheet
1 Tbsp sesame seeds
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