Bring a medium saucepan of salted water to the boil for the spaghetti. Halve the zucchini lengthwise, then thinly slice. Finely grate the zest of one-quarter of the lemon*, then juice the quarter.
Step 2 — Season prawns
Combine the Tuscan seasoning and 2 tsp olive oil in a large bowl. Add the prawns and stir to coat.
Step 3 — 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 10 mins (the spaghetti won't be tender). Reserve 80ml (⅓ cup) cooking water.
Step 4 — Cook prawns
Meanwhile, heat 1 tsp olive oil in a medium frypan over high heat. Cook the prawns, stirring, for 2-3 mins until just cooked through. Remove from the pan.
Step 5 — Cook vegetables
Add the peas and zucchini to the spaghetti and cook for a further 2 mins or until the spaghetti is al dente. Stir in the spinach, then drain. Return the spaghetti and vegetables to the pan.
Step 6 — Get ready to serve
Add the pesto, lemon zest, 2 tsp lemon juice and 1 tbs extra virgin olive oil to the spaghetti and vegetables, then gradually add the reserved cooking water, stirring constantly, until the sauce coats the spaghetti. Taste, then season with salt and pepper. Add the prawns and toss to combine. Divide the spaghetti among bowls to serve.