Zucchini, Carrot, and Parsnip Patties with Lemon Yogurt Sauce

Sauce

• ½ cup plain Greek yogurt
• 2 tablespoons mayonnaise
• 2 tablespoons finely chopped fresh chives
• Finely grated zest of 1 lemon
• 1 teaspoon fresh lemon juice

• Kosher salt
• Freshly ground black pepper
• Extra-virgin olive oil
• 1 cup finely chopped yellow onion
• 1 tablespoon minced garlic
• 2 medium zucchini, about 10 ounces total, trimmed and coarsely grated
• 2 medium carrots, about 10 ounces total, trimmed, peeled, and coarsely grated
• 1 medium parsnip, 5 ounces, trimmed, peeled, and coarsely grated
• 2 large eggs, beaten
• ⅓ cup freshly grated Romano cheese
• ¼ cup all-purpose flour, plus more as needed
• ¼ cup finely chopped fresh chives