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