In a large, deep skillet over medium-high heat, warm 1 tablespoon avocado oil. Add the ground beef and diced onion; cook, breaking the meat into small crumbles, until the onion is soft and the beef is browned with no pink remaining, about 5 to 7 minutes. Drain excess rendered fat so the finished dip does not become greasy.

Return the skillet to medium-low heat. Add the minced garlic and cook just until fragrant, about 30 seconds, then add the cubed Velveeta and the undrained Ro*Tel; stir frequently until the cheese is fully melted, glossy, and the tomato juices are evenly incorporated, 5 to 7 minutes. Keep the heat low because excessive heat can cause the cheese fat to separate.

Serve warm, or transfer the dip to a small slow cooker set to warm for a party. Stir before serving and, if the dip tightens as it sits, restore a scoopable texture with a small splash of milk or reserved tomato liquid.