Cook the pasta to package directions in plenty of salted water. Drain and return the pasta back to the cooking pot, set on the counter.
While the pasta is cooking make the sauce. Heat a 10 inch cast iron skillet over medium-high heat. Add the ground sausage and break apart with a wooden spoon. Cook until no pink remains, about 7-10 minutes. With a slotted spoon, transfer the sausage to a bowl.
Reduce the heat to medium and add the olive oil and onions to the skillet. No need to rinse the skillet, leave a small amount of sausage grease in the pan to enhance the flavor of the onions. Cook the onions for about 5 minutes, until fragrant and translucent. Add the garlic at the last 30 seconds of cooking the onion. Add the spinach, wine and lemon juice to the skillet. Cook a few minutes until the spinach is wilted. Transfer the sausage back into the skillet. Cook until all is hot, season to taste with salt and pepper.
Transfer the sausage mixture into the pasta and toss to combine. Transfer to a large serving dish and top with crumbled feta cheese.