Bring a large pot of water to a boil and salt it well. Cook the pasta until 1 minute short of al dente.
Add the frozen peas to the pot for the last 2 minutes of cooking.
Scoop out 1 cup of the pasta water, then drain the pasta and peas.
In the same pot, melt the butter with the olive oil and garlic over low heat for about 30 seconds.
Add the pasta, peas, lemon zest, 2 tablespoons lemon juice and 1/2 cup of the pasta water. Toss over low heat.
Add the Parmesan a handful at a time, tossing constantly and adding splashes of pasta water until the sauce is glossy and creamy.
Season with salt, plenty of black pepper and more lemon juice to taste. Top with basil or mint and extra Parmesan.