Place the potatoes in a saucepan and just cover with cold water, bring to the boil and simmer for 6-8 minutes or until soft. Drain and set aside.
Meanwhile, heat a tablespoon of oil in a large, deep, non-stick frying pan, approx. 28cm, over a medium heat. Add the onion and fry until soft and transparent. Add the drained potatoes, cook gently for two minutes stirring all the time. Add the spinach and cook until wilted.
Check through the crab meat and discard any pieces of shell. Drain off any liquid. In a large bowl whisk the eggs with the milk, stir through the crab meat and season with salt and pepper. Take the frying pan off the heat and add the potato and spinach mixture into the bowl with the eggs and stir to combine.
Heat a little more oil in the frying pan and add the egg mixture. Move the pan around to let the egg mixture run in under the potatoes and get to the bottom of the pan. Sprinkle over the cheese.
Turn the heat to low, then cook for about 10 minutes until nearly set. Place under a medium grill, and cook for about another 10 minutes until the top is set and golden. Remove from the pan, slice into wedges and serve with a green salad.