Put a large pan of salted water on to boil. Peel and finely slice the shallots. Set a deep frying pan or wok over a medium heat and add 1 tbsp oil and the shallots. Season with a pinch of salt and pepper. Fry for 5 mins, stirring now and then, till starting to soften and brown.
While the shallots fry, peel and crush the garlic. Halve the cherry tomatoes.
Stir the garlic and cherry tomatoes into the shallots with 1 tsp smoked paprika. Finely grate in the zest from the lemon. Cook and stir for 1 min.
Pour in the cherry tomato passata. Cover the pan with a lid (or use a baking tray if you don’t have a lid) and simmer 8-10 mins, stirring now and then, till the sauce starts to thicken a little.
The water should be boiling by now. Add the spaghetti, half cover the pan with a lid and simmer for 8 mins till the spaghetti is tender but still with a little bite.
While the sauce and pasta simmer, whisk the balsamic with ½ tbsp olive oil and a pinch of salt and pepper in a large bowl to make a dressing.
Add the fish pie mix to the tomato sauce and gently turn to mix it in. Pop the lid back on and simmer for 4-5 mins. The fish is cooked through when it flakes easily when pressed with a fork.
Toss the rocket in the salad dressing. Drain the spagheti and add it to the pan with the pasta sauce. Use tongs or two forks to pick the pasta and sauce up and few times to toss it together.
Divide the spaghetti between 2 warm plates or bowls. Garnish with parsley leaves and serve with wedges of lemon for squeezing.