Preheat your oven to 350°F (175°C).
In a skillet, heat the olive oil over medium heat. Add the onion and sauté until translucent, about 5 minutes. Add the minced garlic and sauté for an additional minute until fragrant. Set aside to cool slightly.
In a large mixing bowl, combine the ground turkey (or beef), sautéed onion and garlic, basil pesto, Parmesan cheese, salt, flaxseed meal, Rao's Pasta sauce, and balsamic vinegar. Mix everything until just combined, being careful not to overmix.
Transfer the meat mixture into a meatloaf pan or shape it into a loaf on a baking sheet lined with parchment paper. Smooth the top and shape the sides.
Bake for about 60 minutes, or until the internal temperature reaches 165°F (74°C). Optionally, brush extra pasta sauce on top during the last 15 minutes of baking.
Once baked, remove the meatloaf from the oven and let it rest for about 10 minutes before slicing.
