For the sauce: Fill a pot with water and add the tomatoes, guajillo chili, arbol chili, and garlic cloves. If you want a milder sauce, remove the seeds and stems from the chilis. I removed them for a mild flavor.

Boil for about 10 minutes, then let cool slightly. Blend only the tomatoes, chilis, and garlic. Do not add water; it's not necessary.

Heat a splash of your favorite oil in a skillet. Sauté the onion over medium heat for 3 minutes. Add the can of sliced mushrooms and cook for another 4 to 5 minutes.

Add the spinach and mix well, then pour in the sauce. Season with salt and pepper and mix thoroughly. If you prefer a less acidic sauce, add a little sugar. Cook for another 2 to 3 minutes and serve in warm corn or flour tortillas. Serve with avocado, chopped cilantro, and lime juice if you like a tangy flavor.

This is how it looks after a few minutes.

Assemble and enjoy!