Preheat oven to 425 degrees F. Line a large baking sheet with foil (for easy cleanup) and coat with cooking spray.
In a large bowl, toss together the potatoes, melted butter, garlic infused oil, rosemary, salt and pepper.
Spread potatoes out on the prepared baking sheet. Bake uncovered for about 30 to 35 minutes, or until tender and golden-brown, stirring halfway through.
Remove potatoes from oven and evenly top with the spinach. Return to oven for 1 to 2 minutes more, or until spinach is wilted. Stir the wilted spinach into the potatoes until coated with the butter/oil. Serve.