Begin by bringing a large pot of water to a rolling boil and season it generously with kosher salt. Add the spaghetti and cook until it is just one minute shy of al dente, approximately 7-9 minutes. Before draining, reserve about 1 cup of pasta water. Drain the spaghetti and set it aside, ensuring you finish this step while the pasta is still warm.

In a large skillet, heat 2 tablespoons of extra-virgin olive oil over medium heat. Once the oil shimmers, add the zucchini slices and sauté for about 3-4 minutes until they are tender and starting to brown. Next, add the asparagus and cook for an additional 2-3 minutes until it turns bright green and remains slightly crisp. Remove both vegetables from the skillet and set aside.

In the same skillet, add another tablespoon of olive oil if needed and lower the heat to medium-low. Toss in the diced red onion, leeks, and finely chopped garlic. Stir occasionally, seasoning with a pinch of salt, and cook until the onions are translucent, about 4-5 minutes.

Add the halved grape tomatoes, heavy cream, thawed peas, and a splash of the reserved pasta water to the skillet. Stir vigorously for about 2 minutes until everything is well combined and the sauce thickens slightly. Bring back the sautéed zucchini and asparagus, folding them into the creamy mixture until evenly coated.

Sprinkle finely grated Parmesan cheese over the hot pasta mixture and toss to combine, allowing the cheese to melt into the sauce beautifully. Adjust the seasoning with freshly ground black pepper, lemon juice, and lemon zest to taste.