In a medium saucepan, whisk together the ketchup, brown sugar, apple cider vinegar, Worcestershire sauce, Dijon mustard, garlic powder, and black pepper. Bring the mixture to a gentle simmer over medium heat, stirring occasionally, until the brown sugar is dissolved and the sauce has slightly thickened, about 5-7 minutes. Be careful not to boil.

Add the Lil' Smokies to the simmering sauce. Stir gently to ensure all the sausages are coated. Reduce the heat to low and let the sausages simmer in the sauce for at least 15-20 minutes, allowing them to heat through and absorb the delicious flavors. For an even richer flavor, you can simmer for up to 30 minutes.

Alternatively, for a hands-off approach, combine all sauce ingredients in a slow cooker. Stir well, then add the Lil' Smokies. Cook on low for 2-3 hours or on high for 1-1.5 hours, stirring occasionally, until the sausages are heated through and the sauce is bubbly and slightly thickened.

Once heated and well-coated, carefully transfer the Lil' Smokies and sauce to a serving dish. Serve immediately while warm.