Boil Quinoa. Combine quinoa, salt, and 1 1/2 cups water in a medium saucepan. Bring the mixture to a boil, reduce heat to low, and gently simmer, covered, until the water is absorbed and quinoa is fluffy, about 12 to 15 minutes. Remove from heat and let steam, covered, for 10 minutes. Fluff with a fork and empty quinoa into a large mixing bowl to slightly cool.
Meanwhile, Prepare Cilantro Ranch. In a medium mixing bowl or large liquid measuring cup, combine yogurt, cilantro, oil, vinegar, garlic, and salt and pepper to taste (I usually start with 1/4 tsp. of each); stir with a whisk until smooth. Whisk in 1 to 2 Tbsp. of water to thin to desired consistency.
Assemble Salad. To the bowl of cooled quinoa, add grilled corn, peaches, avocado, Queso Fresco, red onion, and sunflower seeds or pepitas. Add Cilantro Ranch Dressing and toss to combine. Taste and season with extra kosher salt and black pepper as needed. Enjoy warm, chilled, or closer to room temperature.