Blanch the asparagus and peas: Set up a large bowl with ice water. Fill a large saucepan with water and set it over high heat. When the water comes to a boil, add the asparagus and peas.Cook just until tender, 3-5 minutes. The vegetables should look bright green, and still have some texture. Drain and immediately add the vegetables to the bowl of ice water to cool. (Shocking the veggies in ice water stops them from overcooking and preserves their beautiful green color.) Drain.
Make the dressing: In a large mixing bowl, add the vinegar, garlic, a big pinch of salt and pepper, and the sumac, if using. Whisk to combine. Continue whisking as you slowly drizzle in the olive oil. Whisk until the dressing is emulsified.
Mix the salad: To the large bowl with the dressing, add the blanched asparagus and peas. Add the tomatoes, radish, and fresh herbs. Toss to combine. Toss in the feta cheese, if using.
Serve: Taste and adjust seasoning to your liking. Transfer to a serving platter or bowl and serve.
Boil the asparagus and peas until they’re just tender. Maintaining some of their crunch gives the salad a fresh and vibrant taste.
If you like a very lightly dressed salad, set half of the dressing aside before mixing the herbs and vegetables. Any leftover dressing can be used on roasted potatoes or poured over a simple side salad.