Preheat the slow cooker if necessary; see the manufacturer's instructions. Bring a small saucepan of water to the boil, add the rice, bring back to the boil, then simmer for 8–10 minutes or until tender. Meanwhile, butter the inside of a soufflé dish that is 14 cm (5½ inches) across the base and 9 cm (3½ inches) high. Base-line with nonstick baking paper, and arrange tomato slices, overlapping, on top.
Heat the oil in a frying pan, add the onion and fry, stirring, for 5 minutes or until softened and just beginning to turn golden. Stir in the garlic, then add the courgette and spinach and cook for 2 minutes or until the spinach is just wilted.
Beat together the eggs, milk, nutmeg and a little salt and pepper. Drain the rice and stir into the spinach mixture with the egg mixture and mint. Mix well, then spoon into the dish. Cover loosely with buttered foil and lower into the slow cooker pot with foil straps (see
Pour boiling water into the slow cooker pot to come halfway up the sides of the dish. Cover and cook on high for 1½–2 hours or until the tian is set in the middle. Lift out of the slow cooker, leave to stand for 5 minutes then remove the foil, loosen the edge and turn out on to a plate. Cut into wedges and serve warm with salad, if liked.