Grease a baking sheet. In a skillet heat oil over medium-high heat. Add chorizo, onions and garlic and cook, stirring, until chorizo is browned and onion is tender, about 8 minutes. Transfer to a small bowl and let cool completely. Taste and adjust seasoning with salt and pepper, if needed.
On a lightly-floured work surface, stretch bread dough into a rough circle. Using a strainer, drain any excess fat from chorizo mixture, then mound in center of dough. Pull sides of bread up over sausage to completely enclose, squeezing out any air pockets. Pinch edges together to seal. Knead lightly to distribute chorizo evenly throughout loaf and form into a round peasant shape. Transfer to baking sheet, seam-side down, and let rise until doubled, about 40 minutes.
Preheat oven to 400 degree F. Using a razor or serrated knife, cut a shallow "X" in center of dough, and brush with egg wash. Bake bread until brown and firm, about 30 minutes. Let bread cool in pan on a rack 20 minutes, then turn out and let cool. Serve warm or at room temperature.
Yield: 1 loaf