Bring a large pot of salted water to a boil. Add the penne and cook until just tender, about 11 minutes. Drain the pasta in a colander, reserving 250ml of the cooking water, and set aside.
While the water is heating and the pasta is cooking, heat the olive oil in a 14-inch saute pan over medium heat. Add the onions, bell pepper, 1/2 teaspoon salt, and black pepper, and cook until the vegetables are soft, about 4 minutes. Add the sausage and cook, breaking the pieces up with the back of a wooden spoon, until browned, 6 to 8 minutes. Add the garlic and escarole, and cook for 5 minutes longer.
Add the cooked pasta and the reserved cooking water, and stir gently to combine. Simmer just until everything is heated through, about 2 minutes.
Transfer the mixture to a large serving bowl. Add the cheese and crushed red pepper, and toss to combine. Drizzle with the extra-virgin olive oil, and serve immediately.