Lemon Garlic Roasted Pork Loin
1 lemon, zested and halved 1 teaspoon fresh rosemary, or to taste 10 small red potatoes, quartered 2 onions, thickly sliced 3 cloves garlic, roughly chopped 3 pounds boneless pork loin, trimmed 5 stalks white asparagus, halved diagonally 8 carrots, cut diagonally into 1-inch pieces salt and ground black pepper to taste ¼ cup melted butter ¼ cup olive oil, divided