Preheat oven to 350°F. Line a rimmed baking sheet with parchment paper or foil.
Set a medium skillet over medium heat. Add 1 tsp oil and chopped onion and sauté, stirring occasionally, until golden brown, about 10 minutes. Transfer to a plate to cool.
In a large bowl, add all of the meatloaf ingredients and mix just until well combined.
Add meat to the pan and shape it into a meatloaf about 8 inches long, 4 inches wide, and 3 inches tall. Bake uncovered at 350˚F for 40 minutes.
Meanwhile, in a small bowl, add the sauce ingredients and stir to combine.
Spread the sauce over the Meatloaf, then return to the oven and bake an additional 20 minutes or until the internal temperature is 160˚F. Rest the meatloaf for 10-15 minutes before serving.
Serve slices of meatloaf with mashed potatoes, garnished with chopped chives.
To bake in a loaf pan: Line the loaf pan with parchment paper for easier removal. Gently press your meat mixture into your loaf pan and bake following the same instructions, but increase the temperature to 375 F.