In a medium sauce pan heat oil over medium-high heat. Add onion and cook until just browned, about 5 minutes. Add garlic, chili powder, cumin, salt and oregano. Mix well and cook for 30 seconds, stirring constantly. You want to saute your spices for a few seconds because it will give your sauce a more robust flavor.
Stir in tomato sauce and chicken stock. Bring the mixture to a simmer and cook over medium-heat for about 8-10 minutes, stirring occasionally.
Remove the pan from the stove. Let cool for about 5 minutes. Then place ingredients into a blender and process until smooth.
Use right away or refrigerate for up to one week.