Start the pasta water: Fill a large pot with water and bring it to a boil over high heat. Salt the water once it starts to boil.

While the water heats, drain and rinse the beans, finely chop the onion if needed, and zest the lemon. Cut the lemon in half and set it near the stove.

Add the orecchiette to the boiling water and stir well so it does not stick. Cook it until tender but still a little firm in the center, following the package time.

Build the skillet sauce: Set a large skillet over medium heat and add the olive oil.

Put the sausage into the skillet. Use a wooden spoon to break it into small pieces.

Cook the sausage for 4 to 5 minutes, stirring now and then, until it is browned in spots and no pink meat remains.

Add the onion to the skillet with the sausage. Cook for 3 to 4 minutes, stirring often, until the onion looks soft and glossy.

Add the garlic to the skillet. Cook for about 30 seconds, just until it smells fragrant.

Put the drained beans into the skillet. Stir them through the sausage mixture for 1 minute.

Scoop 1 cup of pasta water out of the pot and set it aside. Pour 1/2 cup of that pasta water into the skillet.

Let the skillet mixture simmer for 2 minutes. Press a few of the beans against the side of the skillet with your spoon so they break down and lightly thicken the liquid.

Add the spinach to the skillet a handful at a time. Stir until it wilts down, 1 to 2 minutes.