Bring a pot of salted water to a boil and cook the pasta until al dente. Reserve 1/3 cup of pasta water before draining.

Heat olive oil in a medium-sized casserole or pan over medium heat.

Sauté the halved onions in the oil until they begin to soften and brown slightly.

Add the cooked nopal to the pan with the onions and cook for 3-5 minutes, stirring occasionally.

Add the cooked pasta, salsa verde, and reserved pasta water to the casserole.

Stir everything together to combine and cook for 2 minutes, allowing the flavors to meld.

Serve the pasta hot, topped with crumbled feta cheese.