In a small bowl, mix together the crème fraiche, Parmesan and lemon zest. Sprinkle with black pepper and set aside.
In an 8-inch oven-safe nonstick skillet, melt the butter over medium heat. Add the zucchini, season with salt and pepper and sauté until the zucchini softens and develops some color, about 5 minutes. Add the spinach and cook long enough for the spinach to wilt.
Season the eggs with salt and pepper and give them a good whisk in a medium bowl. Add the eggs to the spinach mixture and, using a wooden spoon, pull the set eggs from the edge of the skillet into the center and allow the bottom to set.
Spoon the crème fraiche mixture on top of the eggs and pop the skillet in the oven. Bake until puffed and golden, about 8 minutes. Cut into 4 wedges.