Steam the cauliflower until tender, 10 to 15 minutes. Transfer to a large bowl, mash and let cool for 10 minutes. Stir in the flour and egg, season with salt and pepper and refrigerate for 15 minutes. Roll 1/4 cupfuls into balls, then flatten into patties, to make a total of 12 to 14. In a skillet, heat 2 tablespoons extra-virgin olive oil over medium-high heat. Working in batches, fry the patties until golden-brown, about 4 minutes on each side. Serve with the salad greens tossed in olive oil and the lemon juice.