Preheat the oven to 375°F (190°C) and grease a 12 x 17-inch rimmed baking sheet; set aside.
Bring a large pot of salted water to a boil and cook the broken lasagna noodles 4–6 minutes until al dente, then drain in a colander.
Return the hot noodles to the pot and toss with 1/2 cup of the basil pesto, grated garlic, fresh thyme leaves, dried oregano, and chili flakes.
Pour in 2 cups whole milk and add the shredded mozzarella; toss until the cheese is mostly melted and coated with the sauce.
Stir in the chopped spinach and season with kosher salt and pepper to taste.
In a small bowl, mix the ricotta with the remaining 1/4 cup basil pesto until combined.
Spread the noodle mixture evenly on the prepared baking sheet. Dollop the pesto-ricotta over the noodles, tucking some underneath the noodles with a spoon.
Pour the 1/2 cup heavy cream evenly over the pan, then sprinkle the shredded provolone, arrange the sliced pepperoni (if using), and finish with the grated Parmesan.
Bake for 20–30 minutes until the cheese is bubbling and lightly golden, then remove from the oven and top with fresh herbs before serving.
