Preheat oven to 375°F (190°C) and line a baking sheet with foil or parchment; lightly grease a loaf pan if using.
Heat oil in a small skillet, sauté diced onion 3–4 minutes, add garlic 30 seconds, then let cool.
Combine breadcrumbs and milk, let soak 2 minutes, then add ground beef, eggs, cooled onion mixture, ketchup, Worcestershire, mustard, paprika, salt, pepper, and optional chili flakes; fold in shredded cheese.
Shape mixture into a 9-inch loaf on the prepared pan; add extra cheese layer in the center if desired.
Lay bacon slices overlapping, wrap around loaf, tucking ends underneath, seam-side down on the pan.
Whisk ketchup, brown sugar, apple cider vinegar, and mustard; brush half over the loaf.
Bake 45 minutes, brush remaining glaze, bake 20–25 more minutes until internal temp reaches 160°F; tent with foil if bacon browns too fast.
Let rest 10 minutes before slicing to redistribute juices.