1. Stir together first 8 ingredients in a big bowl. Divide mixture evenly into 4 portions. Shape each portion into a ball. Place each ball into an 8-ounce microwave-safe coffee mug.
2. Line the bottom of the microwave with a big sheet of wax paper in case juices from the meatloaves bubble out. Place mugs in a circle on top of wax paper. Cover mugs with another big sheet of wax paper. Microwave at MEDIUM-HIGH (70% power) 11 minutes. Cut into meatloaves with a knife and fork. If any are still pink inside, microwave them 30 seconds more and recheck for doneness. Carefully remove each mug from the microwave using oven mitts.
3. Spread 1 tablespoon ketchup over each meatloaf; cover with wax paper, and let stand 2 minutes.