Pour the olive oil into a large, deep skillet. Place the skillet over medium heat and heat until the oil is shimmering. Add the onion and reduce the heat to low. Sprinkle liberally with salt and sweat the onions until translucent, about 7-8 minutes.
Stir the garlic into the onions and saute until fragrant, about 3 minutes more. Stir in the crushed red pepper flakes, and oregano. Increase the heat to medium and saute for 2-3 minutes.
Add the tomatoes to the pan and sprinkle with salt. Cook, stirring constantly until they release most of their juices, about 5 minutes. Pour in the wine and bring the sauce to a boil and reduce to a simmer. Leave the sauce to simmer for 20-30 minutes or until the tomatoes reach a jammy consistency. You want the sauce to be quite thick because the mussels will release a lot of water.
In the last 10 minutes of the sauce's cooking time, bring a large pot of water to a boil. Liberally salt the water and add the pappardelle. Cook the pasta according to the package's directions. Drain and rinse the pasta and set aside.
Once the sauce has cooked down enough, stir in the balsamic vinegar and add the mussels. Bring the sauce back up to a boil, then cover and reduce to a simmer. Cook the mussels until the shells open and the mussels are cooked through, about 3-4 minutes. Sprinkle the finished sauce with fresh basil and parsley.
Place a bed of pasta in four bowls. Spoon the mussels and sauce over top. Finish each bowl with a sprinkling of pecorino cheese and serve immediately with a crisp white wine or a cold lager.