Fry the potatoes. Heat olive oil in a large skillet over medium heat. Add the diced potatoes and cook until golden and crispy on most sides. Cover the pan while they cook to help soften the centers. Transfer the potatoes to a paper towel–lined plate and set aside.
Brown the ground beef. In the same skillet, add the ground chuck. Cook over medium-high heat, breaking it apart with a spoon as it cooks.
Season the meat. Add salt, garlic powder, cumin, and black pepper. Continue cooking until the beef is fully browned.
Add the aromatics. Stir in the minced garlic and diced onion. Cook for a few minutes until the onion becomes soft and fragrant.
Make the tomato sauce. In a blender, combine the Roma tomatoes, serrano chiles, water, a pinch of salt, and Mexican oregano. Blend until smooth.
Combine everything. Pour the tomato sauce into the skillet with the beef. Bring it to a gentle simmer and taste the sauce, adjusting salt if needed.
Add the potatoes. Fold the cooked potatoes back into the skillet, coating them with the sauce.
Simmer the picadillo. Reduce the heat to low and cook for several minutes until the sauce thickens slightly and the flavors come together.
