1. Preheat the oven to 400°F (200°C). Place the poblano peppers on a baking sheet and roast them in the oven for 15-20 minutes, turning occasionally, until the skin is blistered and charred.
2. Remove the peppers from the oven and place them in a covered bowl to steam for 10 minutes. After steaming, peel off the charred skin, remove the seeds, and chop the peppers.
3. In a large skillet, heat the olive oil over medium heat. Add the chopped chicken tenderloin and cook until golden brown and cooked through, about 5-7 minutes.
4. Add the onion and garlic to the skillet and cook, stirring occasionally, until the onion is translucent, about 3-4 minutes.
5. Stir in the cumin, chili powder, and roasted poblano peppers. Cook for an additional 2 minutes to blend the flavors.
6. Pour in the heavy cream and chicken broth, stirring until well combined. Simmer for 5 minutes to thicken the sauce slightly.
7. In a large baking dish, layer half of the chicken mixture, half of the Monterey Jack cheese, and half of the cheddar cheese. Repeat the layers with the remaining chicken mixture and cheeses.
8. Place the casserole in the oven and bake for 20-25 minutes, or until the cheese is bubbly and golden brown.
9. Remove from the oven and let it cool slightly before serving. Garnish with chopped fresh cilantro, if desired.