For stale tortillas: Cut each tortilla into eighths. Spread on a baking sheet. Leave out overnight.
For salsa: Preheat oven to 400 degrees F. Line two baking sheets with foil. Place tomatoes on one pan; drizzle with 2 Tbsp. olive oil and season with 2 tsp. salt. Toss to combine. Place chicken breasts, onion, and garlic on other pan. Drizzle with remaining olive oil; season with 2 tsp. salt and freshly ground black pepper. Roast until chicken is cooked through (165 degrees F), 30 minutes, and tomatoes are slightly charred, 45 minutes. Remove from oven; let cool
When cool enough to handle, peel garlic. Transfer tomatoes, onion, and garlic to a blender; add chicken broth, chipotle chile, and adobo sauce. Blend until smooth, 1 minute. Season salsa to taste with salt and black pepper.
Using two forks or your fingers, shred chicken into 1-inch stringlike pieces.
Meanwhile, in a large saute pan heat vegetable oil over medium heat. Cook tortilla pieces in hot oil, working in two or three batches, until lightly browned on both sides and crisp, about 3 minutes each side. Drain on paper towels; discard remaining oil. Wipe pan clean with a paper towel.
In same pan add salsa; simmer over low heat. Add shredded chicken and fried tortillas; cook until tortillas are soft but not mushy, about 5 minutes. Season to taste with salt and black pepper. Spoon mixture onto a platter. Top with cheese and onion. Drizzle with Mexican crema; sprinkle with cilantro. Serve immediately.