Bring a pot of well-salted water to a boil over high heat. Blanch the mustard greens in the water for 3 minutes. Scoop out the greens and drain it well, squeezing out as much of the water as possible. Chop again and set aside.
Keep the pot of water boiling, and add the spaghetti noodles. Follow the directions on the packet for making the spaghetti. Drain and set aside, retaining about 1 cup of liquid from cooking the noodles.
Fry bacon until just crispy. Add the shallot and saute until soft, adding olive oil if needed.
Add the mustard greens and toss well to break up the clumps.
Combine the ricotta and Parmesan cheeses in a small bowl, and add the lemon zest, salt, and red pepper flakes. Add to the mustard greens mixture in the saute pan and mix well.
Add cooked spaghetti, and some of the pasta water as needed to change the consistency of the sauce. Serve warm.