For thin lamb chops (about 1-1.5 inches thick), you're looking at a cooking time of around 4-6 minutes per side for medium-rare, and 6-8 minutes per side for well-done. But, if you've got thicker chops (1.5-2 inches thick), you'll need to add a few more minutes to each side - we're talking 6-8 minutes per side for medium-rare, and 8-10 minutes per side for well-done.
Now, I know what you're thinking - "What about the internal temperature?" Well, let me tell you, it's a great question, and the answer is 145°F (63°C) for medium-rare, and 160°F (71°C) for well-done. But, if you don't have a meat thermometer, don't worry, you can still use the finger test - just press the chop gently with your finger, and if it feels soft and squishy, it's rare, if it feels firm, it's well-done.
How Do I Cook Lamb Chops in the Oven Perfectly Every Time - Oven Sense
It's also worth noting that the type of lamb you're using can affect the cooking time - for example, grass-fed lamb tends to be leaner, and therefore cooks more quickly than grain-fed lamb. And, if you're using bone-in lamb chops, you'll need to add a few more minutes to the cooking time to account for the bone.
