Preheat the oven to 200°C/fan 180°C/gas mark 6. Slice the fennel into thin strips and toss with the olive oil. Place in the oven for 20 minutes, until softened and slightly browned.
Bring a large pan of water to the boil. Add the pasta and cook for 4 minutes. Meanwhile, pod the broad beans and add them with the peas to the pasta. Cook for a further 4 minutes, until the pasta is just cooked. Drain all the ingredients in the pan, reserving 400ml cooking water, and set aside.
Meanwhile, heat a medium frying pan over a high heat and add the pancetta. Cook for 4-5 minutes, until golden brown all over. Remove from the heat and set aside.
Increase the oven temperature to 220°C/fan 200°C/gas mark 7. Combine the ricotta, mozzarella, lemon zest and cornflour with the reserved pasta cooking water and season well. Mix this with the pasta, broad beans and peas and stir through the roasted fennel and cooked pancetta pieces. Transfer everything to a 2-litre baking dish and sprinkle over the parmesan. Bake for 15-20 minutes, until bubbling and golden brown on top.