Position oven rack in center of oven; preheat oven to 350°.
Make the sauce: heat a large pan over medium heat, add in butter and olive oil; when butter has almost melted, add the onion; cook, stirring often, until translucent, about 3 minutes.
Add in garlic; cook, stirring constantly, until aromatic, about 15 seconds.
Pour in the tomatoes and their juice along with the peas and carrots; stir well and bring mixture to a simmer.
Stir in the thyme, salt, pepper, and nutmeg; simmer just to blend the flavors and boil off a lot of the liquid, about 10 minutes.
You don’t want sauce as thick as ragu—more like a loose tomato sauce but beware of a watery sauce.
Remove pan from heat and set aside.
Cheese filling: whisk the ricotta, eggs, and lemon zest in a big bowl; do not beat—the ricotta should not turn watery.
Prepare asparagus: trim off any beige or woody ends; shave off the outer skin to ensure that the spears will be tender after they are baked.
If you asparagus is not pencil thin, shave down the spears with a vegetable peeler.
Assemble the lasagna in a 13 x 9 inch baking pan as follows: 1 cup tomato sauce spread across the bottom of the pan; 3 no-boil noodles; 1 ½ cups tomato sauce; half the cheese filling (use a rubber spatula to spread it evenly); half the asparagus spears (lay them tip to root in alternating directions); 3 more no-boil noodles; 1 ½ cups tomato sauce, the remaining cheese filling, the remaining asparagus spears, the remaining noodles, and finally the remaining tomato sauce.
Cover pan with a layer of parchment paper, then a layer of foil.
Bake for 35 minutes, then uncover the pan and continue baking until bubbling and gooey, about 10 minutes.