In a large bowl, combine the flour and salt. Cut in the shortening until the mixture resembles coarse crumbs. Add the cold water and mix until a dough forms. Knead for 2 minutes on a lightly floured surface.
Heat the olive oil in a large skillet over medium heat. Add the onion, garlic, bell peppers, jalapeno (if using), cumin and red pepper flakes (if using). Cook until vegetables are tender.
Roll out the dough to 1/8-inch thick. Cut into circles with a biscuit cutter or glass. Place 1 tablespoon of vegetable filling into each circle of dough and fold over to form half moons.
Place empanadas on an ungreased baking sheet and bake at 375°F for 20 minutes or until golden brown.