1. 1. Prepare your oven and baking sheet: Preheat your oven to 375 F (190 C). Line a large baking sheet with parchment paper for easy cleanup.

2. 2. Toss the chicken in buffalo sauce: In a medium bowl, combine the shredded or diced cooked chicken with the buffalo wing sauce and melted butter. Stir well until the chicken is evenly coated.

3. 3. Arrange the first layer of chips and cheese: Spread about half of the tortilla chips in a single layer on your prepared baking sheet. Sprinkle half of the shredded cheddar and Monterey Jack cheeses over this first layer of chips.

4. 4. Add the buffalo chicken and more chips: Distribute half of the buffalo chicken mixture evenly over the cheesy chips. Then, add the remaining tortilla chips on top, creating a second layer.

5. 5. Finish with the remaining chicken and cheese: Scatter the rest of the buffalo chicken over the second layer of chips. Finally, generously sprinkle the remaining cheddar and Monterey Jack cheeses over everything.

6. 6. Bake until golden and bubbly: Place the baking sheet in the preheated oven and bake for 15-20 minutes, or until the cheese is fully melted, bubbly, and slightly golden brown around the edges, and the chips are crispy.

7. 7. Garnish and serve immediately: Once out of the oven, sprinkle the finely diced red onion and chopped fresh cilantro over the hot nachos. Serve immediately with a side of ranch or blue cheese dressing for dipping.