Toast the pine nuts in a dry frypan over medium heat for about 5 minutes, or until fragrant. Remove from heat and set aside to cool.
Heat oil in a frypan over medium heat. Add the red and green capsicums, onion and garlic. Cook and stir until wilted and soft, about 10 minutes. Stir in the tomatoes and continue to cook and stir for another 15 minutes. Mix in the tuna, sugar, cinnamon, nutmeg, salt and pepper. Simmer for about 15 more minutes. Stir in the pine nuts and serve.