Bring a large saucepan of salted water to the boil for the ravioli and peas. Thinly slice the zucchini. Finely chop the onion. Crush or finely chop the garlic. Finely grate the parmesan. Finely grate the zest of half the lemon*, then juice the half.
Step 2 — Cook zucchini mixture
Heat 2 tsp olive oil in a medium deep frypan over medium-high heat. Cook the zucchini and onion, stirring occasionally, for 5-6 mins until softened. Add the garlic and cook, stirring, for 30 secs or until fragrant. Remove from the pan and reserve the pan.
Step 3 — Cook ravioli and peas
Cook the ravioli in the pan of boiling water for 2 mins. Add the peas to the ravioli, return to the boil and cook for a further 1 min or until the ravioli is al dente. Reserve 80ml (⅓ cup) cooking water in a heatproof jug, then drain the ravioli and peas. Crumble 1 stock cube* into the reserved cooking water and stir to dissolve.
Step 4 — Make sauce
Melt 20g butter in the reserved pan over medium heat until the butter is golden brown. Add 2 tsp flour and cook, stirring, for 1 min or until foaming. Gradually add 60ml (¼ cup) milk, stirring constantly to prevent lumps forming. Bring to a simmer and cook, stirring, for 1 min or until thickened.
Step 5 — Toss ravioli
Stir the stock and half the parmesan into the sauce until combined. Add the zucchini mixture, ravioli and peas and gently toss to coat (handle the ravioli with care to ensure they don't break up or burst open). Remove from the heat.
Step 6 — Get ready to serve
Gently stir the truffle mayonnaise and 2 tsp lemon juice* into the ravioli mixture until combined, then season with pepper. Pick the mint leaves, discarding the stems. Divide the ravioli among bowls, scatter over the lemon zest, walnuts, mint and remaining parmesan, to serve.