Fill a medium bowl with water and 2 tablespoons lemon juice; set aside. With a knife, remove all but 1/2 inch stem from artichokes. Cut off sharp tips; remove tough outer leaves, trimming down to yellow inner leaves. Quarter artichokes lengthwise. If they have tough purple chokes, remove with a spoon. Rub artichoke pieces with lemon halves, and place them in lemon water as you work.
In a medium saucepan, combine 3 1/2 quarts water, 2 1/2 tablespoons lemon juice, oregano, garlic, peppercorns, and olive oil. Bring to a boil, and add artichoke quarters. Cook 8 minutes, until tender. Let artichokes cool in the cooking liquid.
Meanwhile, fill a medium bowl with ice water; set aside. Bring a medium saucepan of water to a boil. To peel the pearl onions, boil for 1 minute, and remove with a slotted spoon. When cool enough to handle, peel, leaving root and stem ends intact. Set aside.
Return water to a boil. Add carrots and 1 teaspoon salt. Cook 6 minutes, or until tender. Transfer to bowl of ice water to stop cooking. When carrots have cooled, remove from water with a slotted spoon and set aside. When water has resumed boiling, separately repeat blanching and cooling process with remaining vegetables. Blanch haricots verts and scallions 30 seconds each and peeled pearl onions for 3 minutes.
Just before serving, heat 2 tablespoons butter in a large skillet over medium-high heat. Add vegetables, and saute, stirring, until vegetables are hot and coated with butter. Add stock, parsley, remaining 1/2 teaspoon salt, and pepper; toss and serve.