Mix ground sirloin, bacon, onion, bell pepper, oats, Cheddar cheese, sour cream, Worcestershire sauce, and Cajun seasoning salt in a large bowl; shape into a loaf.
Line 1 1/2-quart loaf pan with bread slices. Put loaf atop the bread.
Bake in the preheated oven until no longer pink in the center, about 15 minutes. An instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C).
Stir tomato sauce and brown sugar together in a saucepan over medium heat; simmer until the sugar dissolves. Add Cheddar cheese in small batches, stirring to melt each batch before adding the next. Stir onion and parsley into the sauce and continue cooking until hot, about 5 minutes. Pour sauce over the meatloaf.
