Place a large frying pan on a medium heat and fry the onion until translucent.
Add the garlic and cook for a minute until fragrant.
Add the harissa paste and pour in the wine if using. Let it simmer for a few minutes until the alcohol cooks off.
Pour in the chopped tomato, add the balsamic vinegar, pour on the stock and simmer for 10 minutes until reduced.
Meanwhile, cook the pasta in a large pan of generously salted boiling water.
Add the shrimp/prawns to the sauce and cook for a few minutes until opaque.
Drain the pasta when it is al dente, ensuring you reserve a few tablespoons of the starchy pasta water first.
Add the lemon zest and juice to the sauce and add a little pasta water to the sauce if needed.
Take the sauce off the heat, add the crumbled feta and toss with the cooked pasta.
Top with fresh parsley and serve immediately.