Place the pears in a saucepan with 1 tbsp of the sugar and 1 tbsp lemon juice. Cook, covered, for 5-10 minutes until just tender. Remove the lid and continue cooking for 2-3 minutes.
Place the bananas in an ovenproof dish and top with the dulce de leche, spreading it all over. Tip over the pears and their juices.
Put the flour in a mixing bowl and rub in the butter ( or use a food processor). Stir in the oats, nuts and remaining sugar. Add the sunflower oil and mix well.
Tip the crumble over the fruit and press down gently. Bake in a preheated oven 200 C Gas 6 for about 45 mins until golden. Leave for at least 10 minutes then serve warm with custard or cream.