Heat the olive oil in a 10-inch nonstick saute pan over medium then add the zucchini and stir until warmed through, 2 to 3 minutes.
Meanwhile, beat the eggs with the milk in a large bowl.
Add the Parmesan and sprinkle with salt and pepper. Stir to combine.
Add the zucchini to the egg mixture. Stir to combine.
Cook pancetta in a 10-inch nonstick saute pan over medium heat for about 5 minutes.
Add the egg and zucchini mixture to the pan. Sprinkle the basil over the top.
Cover and cook over medium-low heat until the edges of the frittata begin to brown and the center is set and slightly puffed, about 8 minutes.
To serve, slide the frittata onto a cutting board and slice into wedges.