Heat oven to 200C/180C fan/gas 6. Heat the oil in a pan and add the leeks, onions and seasoning. Cook for 15-20 mins until soft and beginning to caramelise.
Meanwhile, put the spinach in a colander and pour over a kettle of boiling water. When cool enough to handle, squeeze out as much liquid as possible. Mix the breadcrumbs and cheese together.
Arrange the leek and onion mixture between 4 ovenproof dishes, then scatter with the spinach and pieces of sundried tomato. Make a well in the middle of each dish and crack an egg in it. Season and sprinkle with cheese crumbs. Put the dishes on a baking tray and cook for 12-15 mins, until the whites are set and yolks are cooked to your liking.