Peel and de-vein prawns, leaving tails intact.
Cook pasta in a large saucepan of boiling salted water, following packet directions until tender. Drain.
Meanwhile, heat oil in a large, deep frying pan over medium heat. Add onion. Cook, stirring, for 3 to 4 minutes or until onion has softened. Add garlic and chilli. Cook for 1 minute or until fragrant. Add tomatoes, stock and sugar. Bring to a simmer. Simmer for 5 minutes. Add prawns. Simmer for 5 minutes or until prawns are cooked through and tomato mixture has thickened slightly. Stir in basil.
Add pasta to tomato mixture. Season with salt and pepper. Toss to combine. Serve sprinkled with basil leaves.