Pasta Primavera

In a large pot of boiling salted water, cook pasta, stirring occasionally, until just under al dente according to package directions, 6 to 7 minutes. Reserve 1 1/2 to 2 cups pasta water.

Meanwhile, in a large high-sided skillet over medium-high heat, heat 1/4 cup oil. Cook zucchini, stirring occasionally, until starting to soften and turn lightly golden but still vibrant green, 3 to 4 minutes; season with 1/2 teaspoon salt. Add asparagus, season with 1/2 teaspoon salt, and cook, stirring often, until asparagus is vibrant green and softened, about 4 minutes. Transfer vegetables to a plate.

Reduce heat to medium. Coat skillet with 1 to 2 tablespoons oil, if needed. Add onions and leeks and cook, stirring occasionally, until beginning to wilt and caramelize, about 5 minutes; season with 1 teaspoon salt. Add bell pepper and cook, stirring and reducing heat if onions and leeks start to char, until slightly softened, 3 to 4 minutes more. Add garlic and cook, stirring, until fragrant and onions are translucent, about 2 minutes.

Reduce heat to medium-low. Add tomatoes, cream, peas, and reserved 1/2 cup pasta water. Cook, stirring occasionally, until tomatoes are tender and beginning to burst, 2 to 3 minutes. Add spaghetti, reserved zucchini and asparagus, Parmesan, and a splash of pasta water and cook, tossing to combine and adding more pasta water as needed, until sauce is glossy and cheese is melted.

Stir in lemon zest and juice (if using); season with pepper.