Lightly coat the interior of a 5 to 6-quart slow cooker with nonstick cooking spray. Season the chicken breasts evenly with cumin, garlic powder, onion powder, paprika, 0.5 teaspoon salt, and 0.3 teaspoon black pepper.

Place the seasoned chicken in the bottom of the slow cooker, cover, and cook on Low for 2 to 3 hours (or High for 1.5 hours) until cooked through and tender. Transfer the chicken to a plate, shred finely with two forks, and discard any excess liquid from the pot.

Whisk together the eggs, heavy cream, flour, remaining 0.5 teaspoon salt, and remaining 0.3 teaspoon pepper in a medium bowl until completely smooth.

Layer half of the opened roasted green chiles across the bottom of the slow cooker. Top with half of the shredded chicken and half of both cheeses. Repeat with the remaining chiles, chicken, and cheeses. Pour the egg-cream mixture evenly over the top layer.

Cover and cook on Low for 2 to 2.5 hours, until the egg custard is fully set in the center and the cheese is bubbly and melted around the edges.

Turn off the slow cooker and let the casserole rest uncovered for 10 minutes to firm up before slicing. Garnish with chopped fresh cilantro and serve warm.