Bring a large pot of salted water to a boil on your Blackstone griddle and cook the spaghetti noodles until al dente. Drain and set aside.
Roast the poblano chiles and serrano directly on the griddle until the skins are blistered. Transfer them to a covered container to steam for a few minutes, then peel the poblanos and remove the stems and seeds from all the peppers.
In a blender, combine the roasted poblanos and serrano with the cream cheese, sour cream, chicken bouillon, salt, cilantro, onion, garlic, and milk. Blend until smooth and creamy, adjusting the milk to reach your desired consistency.
Season the chicken thighs with chicken seasoning and Blackstone All-Purpose Seasoning. Cook them on the griddle until golden brown and fully cooked through. Let the chicken rest for a few minutes, then chop it into bite-sized pieces.
Place a cast iron skillet on the griddle and melt the butter. Add the cooked spaghetti noodles, pour in the poblano-serrano sauce, and toss until the pasta is fully coated and heated through.
Serve the creamy poblano spaghetti with the grilled chicken on top. If desired, garnish with fresh cilantro, crumbled cotija cheese, or a squeeze of lime juice.
