Cook potatoes in a pot of boiling salted water until they are tender enough to smash, about 30 minutes.
Transfer the potatoes to a colander and rinse with cold water. Let them cool for 5 minutes.
Lay out the potatoes on a greased baking tray. Flatten each potato into 1/2-inch thickness using a potato masher or a flat kitchen utensil.
Drizzle olive oil over the potatoes. Sprinkle the garlic, parmesan cheese, thyme, salt, and pepper over the potatoes. Lastly, drizzle the lemon juice.
Place the baking tray into the oven on the broil setting until the parmesan cheese turns golden and crispy, about 10 minutes. Use a spatula to scoop them off the baking tray. Serve immediately.