In large pot boil chicken with kosher salt. Once cooked and cooled, shred and set aside.
In blender: mix tomato, garlic, canned chipotle peppers, 1/4 cup of water, black pepper and pinch of salt and sugar.
In skillet sauté sliced onions using Cilantro & Onion Olive Oil until translucent, then add shredded chicken and tomato chipotle sauce. Cook until juices are absorbed into chicken.
Warm tortillas. (If using microwave, stack tortillas on plate and cover with damp towel. Microwave until pliable, 10-15 seconds.)
Spoon 1 Tbsp shredded chicken onto tortilla. Roll tortilla up over filling tightly, then secure with toothpick so filling doesn't fall out during frying. Place on plate and repeat with remaining tortillas.
Add enough Chipotle infused Olive Oil to Dutch oven so it comes up about 2".
Using tongs, carefully slide flautas into oil and fry until golden-brown and crispy, flipping halfway through, 2-4 minutes total.
Transfer flautas to baking sheet and place in oven until all are fried.
Serve warm with shredded lettuce, crema, and avocado slices.