Fill a large bowl with water and lemon juice. Stir well. Cut stems from artichokes to sit flat on your work surface. Peel stems with a paring knife. Transfer artichokes and stems to bowl with lemon water. Working with one artichoke at a time, carefully use a serrated knife to cut off the top third, then use scissors to clip off and discard sharp leaf points, returning each artichoke to the lemon water as you finish.
Fill a large pot with water to a depth of 1 to 2 inches. Cover and bring to a boil. Uncover pot and arrange trimmed artichokes, bottoms up, in a single layer. Add stems around artichokes. Cover pot, reduce heat to medium low and steam until tender, 20 to 40 minutes. Cooking time will vary greatly depending on the size of the artichokes. When the leaves pull out easily and the base can be pierced with a knife, they're ready. Drain well and chop the stems.
Meanwhile, rinse quinoa under cold running water and drain. Combine quinoa and 2 cups water in a medium pot and bring to a boil. Reduce heat to a simmer, cover and cook until quinoa is tender and all the water is absorbed, 15 to 20 minutes. Fluff with a fork and set aside to let cool slightly. Stir in Parmesan, mint, parsley and chopped artichoke stems.
Preheat oven to 400°F. Remove the center leaves from each artichoke and scoop out and discard the fuzzy choke. Place artichokes stem side down in a baking pan and stuff with quinoa mixture, spooning into center and in between leaves. Bake 20 minutes or until heated through.
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