In a medium saucepan heat the oil and add the chopped onions. Sweat the onions, take care not to change the colour and add the salt and pepper. When onions turn translucent add the ginger, nutmeg and the cinnamon. Simmer 2-3 minutes then add the brown sugar and stir gently until all the sugar has melted. Add the vinegar, pears, saffron, orange zest, juice and the raisins. Boil until some liquid has evaporated and left with a syrupy consistency. Lastly, add the chopped tomatoes, simmer for 2-3 minutes. Season to taste and leave to cool completely.