Cook the Pasta - Bring a large pot of salted water to a boil. Cook fettuccine according to package instructions until al dente, about 8-10 minutes. Reserve ½ cup of pasta water, drain, and set aside.

Sauté the Garlic and Spinach - Heat olive oil in a skillet over medium heat. Add garlic and sauté for 1 minute. Add spinach and stir occasionally until wilted, about 2-3 minutes.

Blend the Creamy Sauce - Transfer sautéed spinach and garlic to a blender. Add heavy cream, Parmesan, salt, pepper, nutmeg, and lemon juice. Blend until smooth, return sauce to skillet to warm.

Blanch the Vegetables - Bring water to a boil. Blanch asparagus for 2 minutes, add green peas, and cook for another minute. Drain.

Combine Fettuccine, Sauce, and Vegetables - In the skillet with sauce, add fettuccine and vegetables. Toss over low heat for 2-3 minutes, adding reserved pasta water if needed.

Serve and Garnish - Plate the fettuccine, garnish with basil, toasted nuts, and additional Parmesan if desired.