Special equipment: a muffin pan
Preheat the oven to 350 degrees F.
Warm each tortilla on both sides in a dry skillet over medium heat, about 30 seconds per side. Spray the tortillas with cooking spray. Make a single tear from the edge to the center (like a bicycle spoke) in each tortilla. Nestle the tortillas into muffin cups, overlapping the torn edges so the tortillas fit into the cups.
Bake until the edges are crisp and golden brown, about 12 minutes. Carefully lift out the tortilla cups and invert them so they are resting, bottom up, on the muffin pan. Continue to bake until the bottoms are crisp, about 8 minutes more.
Heat the oil in a large skillet over medium heat. Add the scallions, bell peppers and garlic and cook, stirring occasionally, until slightly softened, about 3 minutes. Increase the heat to medium high and add the shrimp and 1/4 teaspoon salt. Cook, stirring occasionally, until the shrimp are just cooked through, about 3 minutes. Remove from the heat and stir in the lime juice and cilantro.
Spoon the shrimp mixture into the tortilla cups and serve.