Place baby potatoes in a large pot of cold salted water, bring to a boil, and simmer for 15-20 minutes until fork-tender.
Preheat oven to 425°F (220°C) and lightly grease a heavy-duty rimmed baking sheet.
Drain potatoes and arrange on the baking sheet; use a flat-bottomed tool to depress each potato to a thickness of 0.5 inches.
Drizzle potatoes with 2 tablespoons of olive oil, season with garlic powder, half of the salt, and half of the pepper.
Roast potatoes for 15 minutes until the edges are golden and crispy.
Remove potatoes from oven, distribute shredded cheddar cheese evenly over each, and return to the oven for 5 minutes until the cheese is fully melted.
While potatoes finish, pat ribeye cubes dry with paper towels and season with the remaining salt and pepper.
Heat the remaining tablespoon of olive oil in a cast-iron skillet over high heat until shimmering; sear steak bites in a single layer for 2 minutes to achieve a Maillard crust.
Reduce heat to medium, add butter and minced garlic to the skillet, and baste the steak bites for 60 seconds.
Transfer steak bites to a serving platter alongside the cheesy smashed potatoes and garnish with fresh parsley.