Stir 1 tablespoon of the lemon juice into a large bowl of water. Working with 1 artichoke at a time, pull off the dark outer leaves and trim 1/2 inch off the top. Peel the stem. Quarter the artichoke lengthwise, then scrape out the choke with a spoon and drop it into the lemon water. Repeat with the remaining artichokes.
Heat 2 tablespoons of the olive oil in a large heavy saucepan. Add the onion and cook over moderately low heat, stirring, until translucent, about 8 minutes. Drain the artichokes well, add them to the saucepan and season with salt and pepper. Reduce the heat to low and cook, stirring, until just tender, about 12 minutes. Add the peas, fava beans and 2 cups of water. Cover partially and cook over low heat until the vegetables are tender, about 6 minutes.
Add the mint and parsley to the vegetables and season with salt and pepper. Stir in the remaining 3 tablespoons of oil and 2 tablespoons of lemon juice. Serve warm or at room temperature.
The braised vegetables can be refrigerated overnight. Reheat gently before proceeding to Step 3.