Mix the breadcrumbs, cheese, olive oil, parsley, garlic, the juice from 1 1/2 lemons and the salt and pepper in a large bowl until thoroughly combined. The mixture should be slightly moist. If it appears very dry, add a small amount of additional lemon juice.
Cut off the stem of each artichoke, and then trim the tips of the leaves with kitchen shears. Open the leaves with your fingertips and rinse with cold water, holding the leaves open. Working with one at a time, place each artichoke in the center of the bowl of breadcrumb mixture and stuff the mixture into the leaves, holding the leaves open. You may have leftover stuffing, depending on the size of the artichokes. Sprinkle the tops of the artichokes with the juice from the remaining lemon half. Place a lemon slice on top of each artichoke.
Wrap each artichoke in foil and place in a large pot with 3 cups cold water. Bring to a boil. Cover and simmer until the leaves are tender, about 2 hours, depending on the size of the artichokes. (You may need to add more water if the water level gets too low.)