**Sauté the aromatics**:
- Heat a large skillet over medium-high heat.
- If using very lean beef, add the vegetable oil. Otherwise, you can skip the oil.
- Add the diced onion and minced garlic. Sauté for 2–3 minutes until fragrant and slightly softened.
**Brown the beef**:
- Add the ground beef to the skillet. Break it up with a wooden spoon or spatula.
- Cook until the beef is browned, about 5–7 minutes. Drain any excess fat if necessary.
**Add potatoes and carrots**:
- Stir the diced potatoes and carrots (or other vegetables) into the beef mixture.
- Season with cumin, chili powder (if using), salt, and pepper. Sauté for 2 minutes to lightly coat the vegetables and beef in spices.
**Simmer with sauce**:
- Reduce the heat to medium. Stir in the tomato sauce (or puree) and 1 cup of water or beef broth.
- Bring the mixture to a gentle simmer. Cover and cook for 15–20 minutes, or until the potatoes and carrots are tender.
- Check occasionally and add a splash of water or broth if the mixture becomes too dry. Adjust seasonings as needed.
**Serve**:
- Once the vegetables are cooked through and the flavors have melded, remove the skillet from heat.
- Serve hot with warm tortillas, rice, or beans. Garnish with fresh cilantro or chopped green onions if desired.