Bring a medium saucepan of salted water to the boil for the spaghetti. Finely chop the onion. Thinly slice the garlic. Coarsely chop the tomato. Coarsely chop the parsley leaves, discarding the stems.
Step 2 — Cook spaghetti
Add three-quarters of the spaghetti* to the pan of boiling water (if you're tempted to throw in all the spaghetti, just note the dish won't be as saucy). Cook, stirring occasionally, for 12 mins or until al dente. Reserve 60ml (¼ cup) cooking water, then drain the spaghetti.
Step 3 — Cook prawns
Meanwhile, heat 2 tsp olive oil in a medium deep frypan over medium-high heat. Add the prawns, season with salt and pepper and cook, stirring, for 2-3 mins until almost cooked through. Remove from the pan.
Step 4 — Start sauce
Heat 2 tsp olive oil in the same pan over medium-high heat. Cook the onion and garlic, stirring regularly, for 2-3 mins until softened. Add the tomato and cook, stirring, for 2 mins or until softened.
Step 5 — Finish sauce
Add the tomato paste, Tuscan seasoning and ½ tsp chilli flakes* to the tomato mixture (if preferred, omit the chilli when cooking and serve it at the table). Cook, stirring, for 1-2 mins until fragrant. Reduce the heat to medium, add the reserved cooking water, 1 tsp sugar and ½ tsp red wine vinegar and cook, stirring, for 2 mins or until slightly thickened.
Step 6 — Toss spaghetti and serve
Taste the sauce, then season with salt and pepper. Add the prawns and spaghetti to the sauce and cook, tossing, for 1-2 mins until combined and heated through. Add the spinach and toss until slightly wilted. Divide the spaghetti among bowls. Scatter over the parsley to serve.