Preheat the oven to 425°F. Place a wire rack into a rimmed baking sheet and spray with nonstick cooking spray.
Mix shredded chicken and salsa in a bowl. Set aside to absorb the salsa.
Heat olive oil in a large skillet over medium/high heat. Add onion and salt, sauté for 3-4 minutes.
Add garlic and tomatoes, sprinkle with taco seasoning. Cook for 6-8 minutes until tomatoes soften.
Add bell pepper and spinach, cook for 3-4 minutes until spinach wilts. Remove from heat and set aside.
Line the wire rack with tortillas, overlapping to cover completely.
Spread chicken over tortillas, leaving edges. Top with cooked veggies and cheese.
Place remaining tortillas over filling, fold edges over to secure.
Place another baking sheet on top to prevent curling. Bake for 20 minutes.
Remove top sheet, drizzle with olive oil, bake for 8-10 minutes until golden.
Let cool for 5 minutes, then cut into 9 squares.
Top with guacamole, sour cream, and cilantro.