Heat fideos and 3 tablespoons oil in 12-inch nonstick skillet over medium-high heat, stirring constantly, until fideos are deep golden brown but not burnt, 4 to 5 minutes. Transfer fideos to large bowl; set aside. Wipe skillet clean with paper towels.
Heat remaining 1 tablespoon oil in now-empty skillet over medium heat until shimmering. Add tomatoes, onion, and garlic and cook until tomatoes are very soft and have released some of their juices, 8 to 10 minutes.
Process tomato mixture, water, bouillon powder, chipotle, oregano, salt, and pepper in blender until smooth, about 1 minute, scraping down sides of blender as needed. Transfer mixture to 8-cup liquid measuring cup; add extra water as needed to reach 5 cups.
Transfer tomato mixture to again-empty skillet. Using rubber spatula or wooden spoon, gently stir in fideos until fully submerged in tomato mixture. Spread fideos into even layer, and bring to simmer over medium-high heat. Reduce heat to low, cover, and simmer, stirring every 5 minutes, until fideos are tender and sauce is fully absorbed, 20 to 25 minutes, adjusting heat as needed to maintain very gentle simmer. Season with salt and pepper to taste.
Transfer sopa seca to serving bowls. Divide avocado, queso fresco, crema, and cilantro evenly over fideos. Sprinkle with chicharrones, if using. Serve.
