To make Tomato-Corn Relish: Combine all ingredients in bowl. Set aside.To make Rosti: Grate potatoes, carrots, and zucchini onto clean kitchen towel. Wrap towel around vegetables, and squeeze to remove excess liquid. Transfer vegetables to bowl, and stir in onion, flour, and garlic. Fold in eggs, and season with salt and pepper, if desired.Coat large skillet with cooking spray, and heat over medium heat. Spoon 2 Tbs. Rosti mixture for 
each patty, shaping with spoon to make patties. Cook 2 to 3 minutes, or until bottoms are crisp. Carefully flip with spatula, and cook 2 minutes more, or until browned on both sides. Serve with Tomato-Corn Relish.