Halve the peppers and remove the seeds. Grill them in the oven at 220°C (425°F) for 20 min until the skin is charred and dark. Rinse them under cold water for 1 min and peel off the skin. Set aside on a plate.
In a bowl, knead together the flour, water, oil, baking powder, and salt. Let the dough rest for 20 min. Roll out the dough onto a baking sheet lined with baking paper. Prick evenly across the surface several times with a fork.
Spread the grilled peppers (cut into strips), finely chopped garlic, and sliced olives over the dough. Drizzle with olive oil and the pepper juice from grilling. Season with salt to taste.
Bake at 180°C (350°F) for 40 min until the crust is golden brown.
Cool to room temperature and serve, or chill and serve cold as traditionally done in Spain.