About 1 hour before you are ready to make the bread, warm 1/4 c olive oil in a skillet & saute the onions over medium-low heat until they are soft but still slightly crunchy. Add the squash & pepper. Cover & cook for 20 minutes. Add the tomatoes & cook another 3 to 5 minutes. Cool. Stir the yeast into the water & let proof for 10 minutes. Add the biga & mix well. Add the rest of the olive oil. Stir in the cooked vegetables. Add the flour & salt slowly, mixing until the dough comes together. Knead with wet hands until the dough is form, velvet & elastic. Place dough in an oiled bowl, cover & let rise until doubled, about 3 hours. Divide the dough into 4 pieces & shape into long cylinders. Place on floured baking sheets, cover & let rise until well doubled, about an hour. Preheat the oven to 400F. Bake for 35 to 45 minutes, until golden.