Heat 1 tablespoon of the oil in a large frying pan over a moderately high heat. Thickly slice the chorizo and fry for about 3 minutes until crisp and golden.
Add the onion and garlic to the frying pan and continue cooking for 2 minutes until the onion is wilted and coloured but not completely soft. Stir in the paprika and oregano and remove from the heat.
Bring a small pan of water to a gentle simmering point. Crack a quail's egg into a small saucer, then drop it carefully into the simmering water. Leave for 1 minute, then remove with a slotted spoon and place on kitchen paper. Keep the egg warm while you poach the remaining eggs.
Wash and dry the spinach leaves and stir them quickly into the chorizo mixture with the remaining olive oil and the sherry vinegar. Arrange on serving plates, scatter with rinsed and drained capers and top each one with 2—3 quails' eggs. Sprinkle the eggs with the chives and serve immediately.