Prepare the Ranchera Sauce: In a medium saucepan, heat 1 tbsp vegetable oil over medium heat. Add chopped onion and cook until softened, about 3-5 minutes. Add minced garlic and serrano pepper (if using) and cook for 1 minute more until fragrant.

Stir in the diced tomatoes (undrained), half of the chopped cilantro, ground cumin, salt, and black pepper. Bring to a simmer, then reduce heat to low and let it gently cook for 10-15 minutes, allowing flavors to meld. Taste and adjust seasonings.

Fry the Tortillas: Heat 1 tbsp vegetable oil in a large non-stick skillet over medium-high heat. Briefly fry each corn tortilla for 15-30 seconds per side until slightly softened and lightly golden. Remove and set aside on a plate lined with paper towels.

Fry the Eggs: In the same skillet, or a separate one, add 1 tbsp vegetable oil. Fry the eggs to your preferred doneness (sunny-side up is traditional). Season with salt and pepper.

Assemble: Place two fried tortillas on each serving plate. Top each tortilla with a fried egg. Generously spoon the warm ranchera sauce over the eggs. Serve immediately with warm refried beans, sliced avocado, a sprinkle of crumbled cotija cheese, and the remaining fresh cilantro.