Heat the olive oil in a Dutch oven or heavy-based saucepan set over a medium heat.
Add the onion, carrot, celery and pinch of salt, and sweat for 6-8 minutes until softened.
Stir in the garlic, herbs and sugar, and cook for a further 2 minutes. Cover with the crushed tomatoes, stirring well.
Bring to a simmer and cook steadily for 20 minutes, stirring from time to time.
In the meantime, preheat the oven to 180°C (160° fan) | 350F | gas 4. Remove any tough stalks or stems from the chard, and chop the leaves.
Stir the leaves into the tomato sauce, cooking until wilted, about 3 minutes. Season to taste with salt and pepper before setting to one side.
Cook the rigatoni in a large saucepan of salted, boiling water until just 'al dente, ' about 8 minutes. Drain well and set aside.
Coat the inside of a large oval baking dish with cooking spray.
Add the cooked rigatoni to the tomato and chard sauce, stirring thoroughly. Spoon the pasta into the prepared baking dish.
Top with shredded mozzarella and bake for about 20-30 minutes until browned on top and bubbling at the edges.
Remove from the oven and let stand briefly before serving.