Prepare the lemon dressing in a small bowl by whisking together the dill, lemon juice, salt and pepper. Set aside.
Cook the pasta according to package instructions. I prefer my pasta al dente, so I pull it a minute before the earliest cook time recommended.
In a sauté pan, melt butter over low/medium heat. Increase heat to medium and add garlic and onions. Sauté for 3 minutes, stirring as needed.
Add the asparagus. Cook for 4 minutes, stirring as needed. The asparagus should still be a little crunchy and not completely cooked through.
Add green peas. Cook for an additional 2 minutes.
Mix in the cooked, drained pasta.
Add the lemon dressing you prepared and the feta cheese to the pan. Mix until everything is well-combined.
Top with pepper and a couple lemon wedges. Serve immediately.