Roast the serrano pepper and garlic clove on a griddle over medium heat. Remove promptly and set aside. Remove the skin from the garlic.
At low heat on the same griddle, roast the pumpkin seeds, making sure to not overcrowd the griddle. If necessary, roast them in two batches to have an even roasting. Once the seeds start popping, stir them frequently with a wooden spatula until they puff up. They will acquire a medium-golden color. Once they’re done, place them in a bowl to let them cool.
Place the Serrano peppers, garlic clove, roasted pumpkin seeds, one cup of water (or chicken broth), and ½ teaspoon of salt in a blender. Process these ingredients until you have a fine sauce. If needed, you can stop the blender to stir the mixture manually in order to make sure everything gets processed evenly. Once the sauce is ready, set it aside.
Place a paper napkin on a plate and set aside. Heat the vegetable oil in a frying pan over medium-high heat and lightly fry the tortillas. This is a very quick step, since it takes about 15 seconds per each side of the tortilla. You will only warm the tortilla enough to make it pliable. Place the tortilla on the already-prepared dish covered with the paper napkin.
To assemble to your pumpkin seed sauce enchiladas, add 2 tablespoons of crumbled queso fresco on each tortilla and fold them. Place two folded enchiladas on a plate to make one serving.
Heat two tablespoons of lard or vegetable oil in a frying pan over medium heat. Once it is hot, pour in the pumpkin seed (“pipian”) sauce. Gently stir it and reduce the heat; do not let it come to a boil since this will cause the sauce to curdle. Gently simmer it for 5-6 minutes; this last step will make the sauce thicker. If it looks too thick, add a few tablespoons of water or chicken broth. Taste the sauce and add more salt if needed.
Pour some of the pumpkin seed/pipian sauce over the enchiladas, then top them with more queso fresco and some chopped onion.