Preheat oven to 425 degrees F and coat a 12-well muffin tin with oil.
In a large bowl, stir together the flour, water, baking powder, salt, and pepper. The batter will still be quite lumpy at this point, which is fine; just set it aside while you prepare the veggies.
in a large skillet, heat the tablespoon of oil over medium heat. Add the frozen vegetables and allow them to fry, undisturbed, for a couple of minutes, then toss. Continue to fry until heated through and beginning to brown. Keep in mind that frozen veggies are already par cooked, so they may cook twice as fast as fresh vegetables. Season with a pinch of salt.
Give the batter another whisk and try to get most of the remaining lumps out. Add the veggies to the batter and fill the prepared muffin tin with the batter. You can fill each well to the top and make sure each has a good helping of veggies.
Bake for 15 minutes, or until the tops are set and a toothpick inserted into the center of a quiche comes out clean - it might have some crumbs on it but it shouldn't be wet.
Let cool in the tin for 5 minutes, then pop them out to cool on a wire rack.