In a large pot of salted boiling water, cook the pasta al dente. Set aside 1 cup (250 ml) of the cooking water. Drain the pasta and oil lightly.
Meanwhile, in a large non-stick skillet over medium-high heat, soften the peas and garlic clove in 1 tbsp (15 ml) of the oil for 5 minutes. Season with salt and pepper. Set aside half of the peas in a bowl.
In a food processor or blender, purée the remaining peas, garlic, the remaining oil (3 tbsp/45 ml), spinach, cheese, lemon zest and juice until smooth. Season with salt and pepper.
Transfer the pesto to the skillet. Add the pasta and peas and toss to coat. Warm over medium heat and adjust the seasoning, gradually adding cooking water until the sauce is creamy.
Sprinkle with almonds and Parmesan shavings, if desired.