Prepare the Ranchera Sauce: In a frying pan with hot oil over medium heat, sauté the sliced onion, garlic cloves, and halved chiles (serrano and chiles de árbol) until the onion is slightly golden. Lower heat to medium-low, add the guajillo chiles cut into pieces, stirring constantly to avoid burning. When the chiles release their aroma, add the chopped tomatoes and stir. After 5 minutes, add a little water and cover. Cook on very low heat for 10 minutes until chiles and tomatoes are very soft. Turn off heat and let warm.
Blend and Strain the Sauce: Transfer the cooked onion, garlic, and chiles mixture to a blender, add more water as needed, and blend until smooth. Strain the sauce to remove solids and set aside.
Cook the Ground Beef: In a hot pan with very little oil, fry the ground beef over medium heat. Season with salt and pepper. Add chopped garlic and stir constantly to break up the meat and cook evenly until no longer red.
Add Vegetables and Spices: Add chopped onion and green tomato to the cooked meat and fry together for about 10 minutes over medium heat until the tomato softens. Add the crushed cumin, oregano, and clove from the molcajete and fry for one more minute.
Combine with Ranchera Sauce and Nopales: Add the prepared ranchera sauce and cooked nopales to the meat mixture. Season with salt or chicken bouillon powder and add water if necessary to achieve a brothy consistency. Stir well and cover.
Simmer the Stew: Cook the stew covered over medium to medium-low heat for 10 minutes to allow flavors to integrate.
Serve: Serve the beef stew hot with warm corn tortillas, refried beans, and red rice.