Put the artichokes in a steamer basket, stem ends down, and cook until the bottoms are tender when pierced, about 25 minutes. Transfer the artichokes to a plate and let cool.
Meanwhile, in a medium saucepan of boiling salted water, cook the shrimp until opaque throughout, about 2 minutes. Drain and cut into 1/2-inch pieces.
Pull off and reserve 50 of the large outer leaves of the artichokes; reserve the remaining leaves for later use. Pull out the small pointed leaves in the centers and, with a spoon, scrape out the hairy chokes. Cut the artichoke bottoms into 1/2-inch dice. In a large bowl, toss the diced artichokes with the shrimp.
In a small skillet, toast the cumin seeds over moderate heat until fragrant, about 40 seconds. Transfer the seeds to a mortar or a spice grinder and let cool, then grind to a coarse powder. Empty the powder into a small bowl. Stir in the olive oil and lemon juice. Add the dressing to the artichokes and shrimp in the bowl along with the red bell pepper and parsley. Season with salt and pepper and toss well.
Arrange the artichoke leaves on 2 platters. Spoon the shrimp salad onto the base of the leaves and serve chilled or at room temperature.
The recipe can be prepared ahead through Step 4; refrigerate the artichoke leaves and shrimp salad separately overnight.