Toss the ciabatta chunks in 2 tablespoons of the oil, spread out on a baking sheet and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10 minutes or until golden brown.
Meanwhile, in a small bowl, whisk together the remaining oil, the vinegar and wholegrain mustard to make the dressing.
Poach the eggs in a large saucepan of barely simmering water for 5 minutes. Fry the chorizo in a dry frying pan over a medium heat for 3–4 minutes or until crisp and cooked through.
Toss the spinach and chorizo in a bowl with a little of the dressing. Divide between 4 plates, scatter over the ciabatta croûtons and top each salad with a poached egg. Drizzle with the remaining dressing, season to taste with salt and pepper and serve immediately.