In a food processor, add the cilantro, walnuts, and queso fresco. Pulse until coarsely ground, then slowly start adding the olive oil while the processor's still running, until a thick paste forms. Set aside.

In a large cast iron over medium high heat, add the canola oil and minced garlic and saute until tender and fragrant, around one minute. Pour in the tomato sauce, then stir in the cumin and cayenne pepper.

Nestle the serrano pepper, sliced side down, into the tomato sauce, then distribute the cilantro pesto in globs throughout the sauce, using the tip of a spoon to swirl it around in the sauce.

Using a spoon, create a small hollow in the sauce, then crack a single egg into the hollow. Repeat with each egg. Sprinkle with salt, pepper, and queso fresco, then cover and let cook on medium for 5-8 minutes, or to your desired doneness. Serve with fresh cilantro for garnish and flour tortillas for dipping.