Fill the kettle and boil it. Rinse the courgettes. Use a spiraliser to make fine strands of courgetti out of them, or use a julienne peeler to peel fine strips. If you don’t have either gadgets, use a vegetable peeler to peel into thin strips.
Pop the courgetti into a heatproof bowl or dish. Pour over enough hot water from the kettle to cover. Leave to soak for 5 mins. Pop into a colander. Leave to drain well.
Heat the grill to high. Line a grill pan with foil. Rinse and halve the peppers. Scoop out the seeds. Rinse and halve the tomatoes. Pop them all, cut side down, on the foil. Grill for 10 mins till they are charred. Put to one side to cool.
While the peppers and tomatoes are grilling, peel and finely chop the onion. Halve the chilli. Flick out the seeds. Finely chop it. Peel and grate or crush the garlic. Rinse half the rosemary. Pick the leaves off the stalks. Finely chop them.
Warm 1 tbsp olive oil in a pan. Add the onion. Season with salt and pepper. Gently fry for 5 mins till the onion is soft but not coloured. Stir often.
While the onion cooks, pull as much charred skin off the tomatoes and peppers as you can. Roughly chop them. Add the garlic, chilli and most of the rosemary to the onion. Stir and fry for 2 mins till the pan smells sweet.
Stir the tomatoes and peppers into the onion. Pop on the lid. Simmer over a medium heat for 15 mins till the sauce is thick. Stir every so often. Taste the sauce and adjust the seasoning.
Finely grate half the chunk of Parmesan. Divide the drained courgetti between two warm plates. Top with the tomato and pepper sauce and sprinkle with Parmesan to serve.