Heat oil in a large saucepan over medium heat. Add mustard, cumin and fennel seeds, and stir for 1 minute or until mustard seeds begin to pop. Add onion, garlic and ginger, and cook, stirring constantly, until softened. Add spices, Swiss Chard, rice, 200ml (7 fl. oz) water, coriander, curry leaves and tomato. Cook, stirring constantly, for 2 minutes to coat the rice in spices. Season.