Step 1Heat the oven to 350 degrees.
Step 2In a sauté pan heated over medium-high heat, add the oil along with the carrots, squash, bell pepper and onion. Cook, stirring frequently, until the vegetables are tender, about 5 minutes. Remove from heat.
Step 3In a large bowl, knead together the ground turkey, eggs, bread crumbs, sautéed vegetables, one-half cup marinara and the salt and pepper to form a uniform mixture. Because marinara sauce will vary in saltiness by brand, to check the seasoning, break off a little of the meatloaf mixture and sauté it until browned, then taste it and adjust the seasoning if needed with extra salt and/or pepper.
Step 4Place the mixture in a loaf pan, mounding the loaf to mimic the shape of a loaf of bread. Bake the loaf until set and a thermometer inserted in the center of the loaf reaches 165 degrees, about 1 hour. Meanwhile, warm the remaining 1 cup marinara sauce.
Step 5Remove from heat and cool slightly on a rack to set before serving. Serve the meatloaf warm, with the extra marinara brushed over the loaf before slicing or ladled over the slices as they are served.