Fill a Dutch oven a little less than halfway with the oil. Bring to 375 degrees F over medium-high heat. Place a cooling rack on a baking sheet.
Whisk the flour, muffin mix, cornstarch and a pinch of salt in a large bowl. Slowly whisk in the seltzer, trying to avoid any lumps, and stopping when your mixture is a touch thinner than pancake batter. Add the vegetables to the batter one type at a time—the vegetables will all have different cooking times—and toss to coat. Add the vegetables to the oil a few at a time. Fry, turning frequently, until they are golden brown and crispy, 2 to 3 minutes. Remove to the cooling rack and repeat with the remaining vegetables. Sprinkle with salt as they come out of the oil.
Stir together the mayonnaise, chives, lemon, sriracha and ginger in a small bowl. Serve the veggie fritters hot with the chive dipping sauce.