Preheat the oven to 475°F.
Rinse and scrub the red potatoes under cold water to remove any dirt. Coat a rimmed baking sheet with non-stick cooking spray.
Bring a medium pot of water to a rolling boil. Add a generous pinch of salt. Carefully add the potatoes and boil for 15 minutes, until they're tender enough to be pierced with a fork.
While the potatoes are boiling, melt the butter in a small microwave-safe bowl. Stir in the minced garlic and Old Bay seasoning.
Drain the potatoes and let dry.
In a large bowl, whisk together the olive oil with a pinch of salt and pepper. Toss the drained potatoes in the oil until they're evenly coated.
Arrange the potatoes on the prepared baking sheet. With a heavy-bottomed glass or potato masher, gently press down (i.e., smash) on each potato until it's about 1/2-inch thick.
Brush each smashed potato generously with the garlic butter mixture. This will infuse them with flavor and help them crisp up in the oven.
Roast the potatoes for 15 minutes, until their edges turn golden brown. Remove from the oven.
Sprinkle a bit of the chives onto each potato, followed by a generous amount of the shredded cheese blend.
Return the baking sheet to the oven for another 5–7 minutes, until the cheese is melted and bubbly.