Heat the oil in a large saute pan over high heat. Add the zucchini, peppers, onion and salt and pepper, to taste, and cook until almost soft, 5 minutes. Stir in the garlic and 1/4 teaspoon the red pepper flakes and cook for 30 seconds. Set aside to cool.
Whisk together the eggs and herbs in a large bowl. Add the meat, bread crumbs, cheese, 1/2 cup of the ketchup and 2 tablespoons of the balsamic vinegar and the vegetables and mix until just combined. Mold the meatloaf on a baking sheet lined with parchment paper. Whisk together the remaining ketchup and balsamic vinegar in a small bowl then brush the mixture over the entire loaf. Bake the meatloaf for approximately 1 to 1 1/4 hours. Remove from the oven and let rest 10 minutes before slicing.