Bring a medium pot of generously salted water to a boil and cook the pasta according to the package label instructions. Drain, reserving 1 cup of pasta cooking water.
Meanwhile, heat the oil in a 12-inch skillet over medium-high heat. Once hot, add the sausage and use a wooden spoon to break the sausage up into very small crumbles (the smaller the better for saucier sauce). Cook, stirring regularly, until lightly golden brown and cooked through, about 10 minutes. Reduce the heat to medium, add the shallots and garlic and cook, stirring often, until the shallots are softened, about 3 minutes.
Stir in the Calabrian chilies, fennel, black pepper and tomato paste until the spices and tomato paste are evenly distributed, about 1 minute. Fold in the cherry tomatoes and cook, stirring often, until they burst and the mixture becomes saucy, 5 to 7 minutes. Turn off the heat until ready to serve.
When ready to serve, turn the heat to medium-low. Add the butter and beans; stir until the butter has melted and incorporated and the beans are warmed through. Add the pasta to the sauce and, in small splashes, add as much reserved pasta liquid as needed to reach a saucy consistency. Transfer to plates, sprinkle with oregano and more black pepper, if desired, and serve.