Cook 12 oz. spaghetti in a large pot of boiling salted water until very al dente, about 1 minute less than package directions. Drain, reserving 2 cups pasta cooking liquid.

Meanwhile, place 4 oz. pancetta (Italian bacon), cut into ¼" pieces, in a cold, dry medium Dutch oven or other heavy pot and set over medium-high heat. Cook pancetta, stirring often, until browned and crisp, about 5 minutes. Using a slotted spoon, transfer pancetta to a small bowl, leaving fat behind in pot.

Pour extra-virgin olive oil into fat in pot so you have 3 Tbsp. total. Arrange two 12-oz. jars marinated quartered artichoke hearts, drained, in a single layer in pot and cook over medium-high heat, undisturbed, until golden brown underneath, 6–8 minutes. Add 4 garlic cloves, thinly sliced, and ¼ tsp. crushed red pepper flakes and season with freshly ground black pepper. Cook, stirring often, until fragrant, about 2 minutes.

Reduce heat to medium. Add pasta, 2 oz. Parmesan, finely grated (about 1 cup), 4 Tbsp. unsalted butter, and 1 cup reserved pasta cooking liquid; season with salt. Cook, tossing constantly and gradually pouring in more pasta cooking liquid until all 2 cups have been incorporated and a thick, glossy sauce forms, about 2 minutes. Remove pot from heat and mix ¼ cup finely chopped parsley, 2 Tbsp. fresh lemon juice, and pancetta into pasta; season with more salt and black pepper if needed. Divide among shallow bowls.