Bring a large pot of salted water to a boil. Preheat oven to 350C. Pick up one stalk of asparagus by the root end, and snap off the woody end (usually about 1½ inches or so). Line up the snapped asparagus with the rest of the bunch and use a knife to cut them all to the same size.
When water is at a rolling boil, add pasta and cook for 8-10 minutes.
Toss Asparagus in some olive oil and season with salt and pepper. Spread on sheet pan and roast for 10 minutes.
Heat a medium-sized pan on medium-high heat. Add oil and paprika. When you can smell the paprika, add the onions and garlic and cook until softened, 5-6 minutes. Add lemon juice to pan and remove from heat.
In large bowl, combine pasta with vegetables, cooked onion, roasted asparagus, feta, and balsamic vinegar. Toss and season with salt and pepper to taste.