Preheat oven to 350 degrees F (175 degrees C). Spray a 9x11-inch baking dish with cooking spray.
Cut 3/4 each of onion, green bell pepper, red bell pepper, and yellow bell pepper into thin slices. Dice remaining 1/4 of onion and peppers.
Mix ground beef, diced onion and peppers, tomato sauce, crushed crackers, brown sugar, egg, Worcestershire sauce, chicken stock, olive oil, steak seasoning, garlic, and pepper together in a bowl until well-combined.
Spread 1/2 of the beef mixture into the bottom of the prepared baking dish. Top meat with sliced onion and peppers, leaving a 1-inch border. Spread remaining beef mixture over vegetables, tucking in sides to seal vegetables in the center of the meatloaf. Pour ketchup over the top of the meatloaf.
Bake in the preheated oven until no longer pink in the center, about 1 hour. An instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C).