Warm a large, deep skillet over medium-high flame and add a splash of oil. Sauté the bacon pieces until they become crisp and golden. Remove them onto a plate lined with paper towel to drain excess grease.
Discard half of the rendered bacon fat from the skillet, keeping the remaining. Add another small drizzle of oil, then brown the ground beef, breaking it into fine crumbles as it cooks. Near the end of browning, mix in the diced onion, paprika, and black pepper. Continue sautéing until the onion becomes translucent.
Pour in the tomato sauce, beef stock, and Dijon mustard. Stir thoroughly to integrate the ingredients.
Introduce the dry elbow macaroni to the skillet, cover with a lid, and bring the mixture to a gentle boil. Reduce the heat to a low simmer, give it a quick stir, cover again, and allow it to cook for 15 minutes, or until the pasta reaches desired tenderness.
Uncover the skillet, stir again, and blend in the shredded cheddar, half of the reserved bacon, and the relish. Stir continuously until the cheese melts and coats everything evenly.
For an extra cheesy finish, sprinkle a layer of additional shredded cheddar over the top, cover the pan again, and let the cheese melt completely. Garnish with the rest of the crispy bacon and sliced scallions before serving.