Put onion, tomatoes, garlic, salt, pepper and cilantro into blender container. Buzz, buzz, for a few seconds until completely liquified. Set aside.
Melt butter and oil together in a deep skillet over medium-high heat. Add noodles, saute while gently tossing with spatula and large spoon, or tongs. Continue carefully tossing and moving the noodles until they are toasty, golden brown, about 5 minutes.
Add blender-buzzed tomato mixture and fold gently to distribute. Top off with just enough chicken broth to cover noodles. Reduce heat, so mixture just simmers. Cover and cook about 8-10 minutes until most of the liquid is absorbed and noodles are perfectly al dente.
Scoop appetizer size servings into bowls or small plates and top with avocado chunks, cheese and cilantro or your favorite topping combinations. Fantastico with a side of cerveza or margaritas and, of course, some rousing mariachi music. Salud!