Preheat oven to 180 degrees C. Bring the pie shell to room temperature.
Heat the olive oil in a frypan over medium heat; add the onion and cook until onion becomes transparent, about 5 minutes. Combine the spinach with the onion, cover the frypan; turn off the heat and set aside.
Press the shell to fit into a 23cm pie dish. Trim the edges.
Beat the eggs in a large bowl until light coloured and frothy. Add the garlic, thyme, basil, cheeses and spinach mixture and stir until well blended. Season to taste with salt and pepper. Pour the spinach mixture into the prepared pie shell.
Bake in preheated oven until the top is golden brown and an inserted tooth pick comes out clean, about 50 minutes.