For the creamy tahini sauce:
2 tablespoons extra-virgin olive oil (EVOO)
3 cloves garlic, crushed and chopped
1 tablespoon harissa paste or rose harissa or 1 fresh hot chili pepper, chopped
⅔ to ¾ cup tahini (ground sesame sauce)
Salt and fine black or white pepper
Juice of 1 lemon
About ¾ cup water
For the pasta:
1 bunch asparagus, cut on the bias into large pieces
1 bunch scallions or 4 spring onions, cut on the bias into large pieces
Non-aerosol olive oil spray
Salt and pepper
1 lemon, halved
1 pound gigli (aka campanelle), a lily-shaped short-cut pasta or other short pasta
For the sauce, warm oil in a small skillet over medium heat and swirl garlic a minute or so, add harissa or fresh chili and combine, cool a bit. Place in food processor with tahini, season with salt and pepper, add juice of 1 lemon and turn on processor, then stream in water to form smooth sauce, transfer to a bowl.
Hold a spear of asparagus at both ends, bend and snap. The end is a measure for where to trim the bunch. Ends can be cooked in stock and softened to puree for soup.
Trims tough tops and roots of scallions or spring onions.
Heat a cast iron skillet or large nonstick skillet over medium-high to high heat with a spray of oil. Add the asparagus and scallions or spring onions, in 2 batches if necessary, and season with salt, brown 2 to 3 minutes, turn and cover 1 to 2 minutes more. Cook the cut lemon as well to char. Douse the cooked asparagus and spring onions with ½ the charred lemon.
Undercook pasta by 1 minute in salted boiling water, reserve ¾ cup boiling water and drain. Return to hot pot and combine with tahini sauce and add the hot water as needed to thin a bit to coat pasta with velvety sauce. Taste and adjust salt as needed. Add half the asparagus and onions and the remaining juice of ½ charred lemon. Transfer to serving bowl and top with remaining asparagus and scallions or spring onions and za'atar.