Place zucchini pieces on a clean towel and sprinkle with a pinch of salt; let sit 5 to 10 minutes to draw out moisture, then pat dry.
Bring a pot of salted water to a boil and cook pasta according to package instructions until al dente; drain and rinse immediately with cold water.
Combine the cold pasta, chopped spinach, and diced artichoke hearts in a large mixing bowl.
Heat 1 tablespoon olive oil in a large skillet over medium heat. Add diced onions with a pinch of salt and sauté until softened, then transfer to the mixing bowl.
Add lemon halves and zucchini cut side down to the skillet. Cook zucchini undisturbed for 3 minutes until caramelized, then flip and cook another 3 minutes.
Cook lemon halves undisturbed until bottoms caramelize, about 5 to 6 minutes; remove from heat and add zucchini to the mixing bowl.
In a blender cup, combine basil, parsley, lemon zest, garlic, pepitas, yogurt, miso paste, remaining olive oil, juice of cooked lemon, and a pinch of salt; blend until smooth.
Pour half of the dressing over the pasta mixture and toss well to combine; add more dressing as desired or serve on the side.