Turn the oven to the broiler setting.
Slice 1 lemon horizontally and place the slices on a baking sheet lined with parchment paper. Broil until the lemons turn dark on the edges. Remove from the oven and let cool.
Fill a large bowl with water and the juice of the remaining lemon. Cut the top of the artichokes and remove the outer leaves almost down to the core. Cut the artichokes in half and take out the fuzzy insides with a spoon. Cut each half once more and place each quarter immediately in the lemon water to prevent oxidation.
Heat up the olive oil in a large pan and cook the onion and garlic until tender, about 5 minutes. Add the artichokes to the pan along with the chicken stock and 1/2 cup water. Season with salt and pepper. Cover with a lid and cook for 30 minutes.
Place the artichokes and onions on a serving plate. Add the olives, feta cheese, lemon slices and chopped thyme, placing them at random. Drizzle with the vinegar. Add salt and pepper to taste.