Preheat your oven to 425 degrees F. Heat your oil in a large cast iron sauté pan over medium-high heat. Add the onion and cook down until translucent. Add the zucchini, bell peppers and carrots and cook until soft. Add garlic last and season with salt and pepper. Turn off heat and let cool.
Whisk the egg and add to a large bowl with the herbs, turkey, breadcrumbs, and cheese. Add 1/2 cup of ketchup and 2 tablespoons of balsamic vinegar to your cooling vegetables. Mix in your cooled veggies to your large bowl with turkey until combined.
Gently press the mixture into a 9 by 13 rectangle pan. Whisk together your remaining ketchup and balsamic vinegar to make a sauce. Add the sauce to the top of your meatloaf and spread to create an even layer.
Bake your meatloaf in the oven uncovered for 60 to 75 minutes. Let rest for 10 minutes before slicing.