To make flatbreads: Stir together flour, baking powder, and salt in a medium bowl. Stir in 3 tablespoons oil and 3/4 cup warm water until combined. Turn out dough onto a clean surface and knead until smooth, 5 minutes. Cover with a bowl and let rest 30 minutes.
Meanwhile, make the filling: Steam 3 cups cauliflower florets until soft, 8 to 10 minutes, then transfer to a medium bowl and mash. Heat oil in a medium skillet over medium heat and toast cumin seeds until fragrant, about 30 seconds, before stirring in coriander and turmeric. Stir in spinach and cook until just wilted. Remove mixture from heat and stir in cauliflower and peas (no need to thaw before using). Season with salt.
Assemble flatbreads: Divide dough into 8 balls and roll out into 6-inch rounds. Add filling to half of the round, fold in half and seal edge with a fork. Heat a cast-iron skillet over medium heat with 1 tablespoon of olive oil and cook rounds until slightly puffed and golden, 2-3 minutes. Flip and cook 2-3 minutes more. Serve pockets cut in half with orange slices. (Serving size: 2 flatbreads, 1 orange)