Open can of tomato and place into a blender.
Slice onions and set aside. Mince garlic and set aside. Remove stems from chiles and cut chiles into roughly 1-inch pieces.
Add 1 tbsp of oil to a stockpot and set heat to medium-high.
Add onion and chiles. Cook, stirring frequently until onion turns golden brown and chiles are aromatic and softened. Add garlic and stir for 1 more minute. Transfer onions and chile to the blender.
Add half of the stock, Mexican Oregano, and a pinch of salt to the blender. Blend until completely smooth.
Return pot to the stove and set over medium heat.
Add 2 more tbsp oil. Use a medium-mesh strainer to strain the puree directly to the pan.
Bring to a simmer and stir puree frequently to avoid burning or sticking to the pan.
Add the remaining 4 cups of stock to the pan and bring to a simmer. Taste and add more salt if needed.
Ladle soup into bowls and top with broken tortilla chips and your favorite garnishes.