In a large skillet, cook the chorizo over medium-high heat, breaking it up into small pieces as it cooks. Once cooked, transfer to a plate.
In the same skillet, add the olive oil to any remaining chorizo grease. Add the onion, bell pepper and potatoes, and season with salt and pepper. Cook, stirring occasionally, until the vegetables are softened, about 10 to 12 minutes.
Add the garlic and cook for 1 minute more.
In a medium bowl, add the eggs and milk; whisk well to combine.
Add the butter to a nonstick skillet over medium-low heat, then add the eggs and cook, stirring occasionally, until fully cooked and scrambled.
To assemble the breakfast burritos: Place the tortillas on a plate, cover with a damp paper towel and microwave for 30 seconds. Microwave for an additional 15 seconds, if necessary. Tortillas are easier to roll when warm.
Lay out the tortillas and fill ⅓ of each tortilla with scrambled eggs, chorizo, potatoes, cheese and avocado slices. The amount of each component you add to one burrito is up to you and depends on the size of the tortillas.
Roll the tortilla once, fold in the sides, then roll the burrito the rest of the way.
Serve topped with sour cream and salsa. Enjoy!