Bring 2 cups lightly salted water to a boil in a large wide pan. Add greens and cook until tender, 10 to 12 minutes. Drain, rinse with cold water and press out excess moisture. Set aside. (we take the stems out)
Put a large pot of lightly salted water on to boil for cooking pasta.
OPTIONAL: Cook pancetta (or bacon) in a large nonstick skillet over medium heat, stirring often, until golden, 5 minutes. Drain; discard fat.
Add oil to the pan and heat over medium heat. Add onion and scapes and cook, stirring often, until softened, 3 to 5 minutes. Add crushed red pepper; cook, stirring, for 30 to 60 seconds. Add the pancetta (or bacon), tomatoes and water; bring to a simmer, mashing the tomatoes a bit with spoon. Reduce heat to medium-low and simmer, uncovered, until thick.
About 10 minutes before the sauce is ready, cook pasta in the boiling water, stirring often, until just tender, 8 to 10 minutes. Reserve 1/4 cup of the cooking water and drain the pasta.
Add the pasta, greens and reserved pasta-cooking water to the tomato sauce. Cook together for about a minute or so. Top with cheese.