Directions for Chile Base
1. Heat a large (12-inch) cast-iron skillet over medium heat. About 4 minutes, add chiles; cook, turning occasionally, until fragrant. Should be lightly toasted. Transfer to a blender; add the 1 1/2 cups boiling water. Mixture should stand for about 30 minutes. Add tomato sauce, cilantro, and salt and process until smooth for about 20 seconds. Set aside.
Directions for Fideo Filling
1. Heat oil in a large cast-iron skillet over medium-high heat. Add chorizo. Cook, stirring occasionally, until crumbled and browned for about 6 minutes. Stir in fideo, garlic, bay leaf, and chile de árbol. Cook, stirring occasionally. Fideo should be lightly toasted and turning opaque, 4 to 5 minutes.
2. Stir in chile base. Reduce heat to low. Cover and cook until fideo is tender. Liquid should be fully absorbed within 15 to 20 minutes, stirring once after 8 minutes. Remove and discard bay leaf and chile de árbol. Transfer mixture to a medium bowl, and stir in cilantro. Let cool 20 minutes. Stir in Monterey Jack cheese.
3. Top each tortilla with 1/3 cup fideo filling; fold each tortilla in half, pressing gently. Heat a large cast-iron skillet or grill pan over medium-high heat. Toast tacos until tortilla is lightly charred and filling is warmed through, 2 to 3 minutes per side. Be sure to work in batches. Top tacos with Mexican crema, avocado slices, and crumbled queso fresco. Garnish with cilantro.
4. Serve immediately.