Heat oil in a large sauté pan over medium flame. While oil is still warming, add guanciale or pancetta to pan and toss to coat with oil. Add pepper flakes and black pepper. Cook, stirring occasionally, for about 5 minutes, then add onion and cook until translucent and softened, about 5 minutes, stirring occasionally.
Meanwhile, empty canned tomatoes into a medium bowl. Crush tomatoes by hand, one at a time, into the bowl (you remembered to wash your hands, right?). Aim them as best you can, knowing that tomato bits will squirt in unexpected directions.
Add wine to pan and cook, stirring and scraping up any browned bits, until wine is mostly evaporated. Add tomatoes and all their juices to pan, stirring to combine thoroughly. Mash any big chunks of tomato with a wooden spoon. Simmer uncovered over medium-low for 15 – 20 minutes.
Meanwhile, cook the pasta until it's about 2 minutes short of being al denté according to package directions. Drain, reserving a couple ladles of pasta water, and add the pasta to the pan, stirring to coat the pasta with the sauce. If pasta seems dry, stir in some pasta water—I added a few tablespoons. Cook until pasta is al denté, about 2 minutes.
Stir in 1/2 cup of Pecorino Romano. Taste and season with salt, if needed. I didn't need to. Divide among 4 pasta bowls, being sure everyone gets a share of the pancetta, onion and any chunks of tomato still lurking in the pan. Top with additional grated Pecorino and serve.