Crushed tortilla chips,shredded pepper jack cheese, and cilantro, optional for serving
Heat oil over medium-high heat in a large stockpot or Dutch oven. Sauté the carrots, celery, and onion until beginning to soften, about 7 minutes. Add the garlic and cook for 1 minute. Sprinkle the flour over the vegetables and cook for 1 minute, stirring continually. Slowly stir in the broth and bring to boil. Reduce heat and simmer, partially covered, for 10 minutes.
Add the chicken, noodles, evaporated milk, salt, oregano, and pepper. Stir to combine. Cook the soup for 10 minutes, until the noodles are al dente.
Serve warm, garnished with crushed tortilla chips, shredded cheese, and cilantro.