Brush the pan with the remaining 1 teaspoon oil; heat over medium heat. Pour in the egg mixture and tilt to distribute evenly. Reduce the heat to medium-low and cook until the bottom is light golden, lifting the edges to allow uncooked egg to flow underneath, 3 to 4 minutes. Place the pan under the broiler and cook until the top is set, 1 1/2 to 2 1/2 minutes. Slide the frittata onto a platter and cut into wedges.