1. Preheat oven to 400 degrees. Lightly brush both sides of tortillas with 2 teaspoons oil and place on a rimmed baking sheet. Bake until golden and crisp, 10 minutes. Divide cheese among tortillas and return to oven. Bake until cheese is bubbling, about 3 minutes. Remove from oven and set aside.

2. In a large skillet, heat 1 teaspoon oil over medium-high. Add half the red onion and cook until softened, about 3 minutes. Add chili powder and garlic and cook until fragrant, 30 seconds. Add chicken and cup water and season with salt and pepper. Cook, stirring frequently, until chicken is warmed through and water is almost evaporated, 2 minutes. Stir in 1 teaspoon lime juice and remove from heat.

3. In a large bowl, combine lettuce and 1 tablespoon lime juice; season with salt and pepper. Toss well to coat and divide among tortillas. Top each tortilla with chicken mixture, tomato, avocado, remaining onion, and cilantro.