To make the glaze: Mix together 1/3 cup soup, ketchup, brown sugar and 1 1/2 tsp mustard until smooth. Set aside.
Preheat the oven to 350°F. Line a standard baking sheet with aluminum foil and spray with cooking spray.
In a stove top pan, saute the diced onions and peppers in a few drizzles of olive oil until softened and translucent around 3 minutes. Season with salt and black pepper to your taste, then set aside to cool slightly.
While vegetables cook, in a medium mixing bowl, mix together beef, Panko, 3/4 cup soup, buttermilk, eggs, mustard, Worcestershire, barbecue seasoning and pepper. Add cooked peppers and onions. Mix well.
Using your hands, roughly form the meat mixture into a loaf shape in the bowl. Slide the loaf onto the center of prepared baking sheet.
Pat the meat-loaf into an oblong loaf shape approximately 2 1/2 inches thick. It's important to make the loaf proportional so it will cook evenly. Pour half of the glaze over the top.
Bake for 55 minutes. Remove from the oven drizzle with remaining glaze.
Return the meat-loaf to the oven and bake for another 10-15 minutes or until juices run clear.
Rest on the counter for 15 minutes before serving.
If you use ground beef with a higher fat content [ ie. 80/20] the meatloaf should be prepared in a baking dish or loaf pan to better keep it's shape.