Preheat the oven to 425°. Bring a large pot of salted water to a boil. Add the pasta and cook according to the package directions. Reserve 1 cup of pasta cooking water for later then drain the pasta, without rinsing.
Meanwhile, toss the chicken with 1 Tablespoon olive oil, garlic powder, onion powder, Italian seasoning, red pepper flakes, salt, and pepper.
Drizzle the remaining 1 Tablespoon of olive in the bottom of a large, oven-safe skillet, like a cast-iron skillet, over medium-high heat.
Once it’s hot and shimmering, pan fry the chicken for 8-10 minutes, flipping halfway through, until golden brown on the outside and the internal temperature reaches just below 165°F. The chicken will continue to cook when it’s baked so it doesn’t need to be fully cooked (I pulled mine off the heat at 145°F). Add a splash of water as needed to the pan if it’s becoming too brown before the chicken is cooked through. Transfer the chicken to a clean cutting board to rest.
In the same pan, add 1 Tablespoon of butter and stir to melt over medium heat, scraping some of the brown bits from the chicken as you go. Add the shallot and cook for 2-3 minutes, until soft and translucent. Stir in the garlic and cook for another 1-2 minutes, until fragrant.
Add the remaining 3 Tablespoons of butter and stir to melt. Sprinkle the flour on top and stir to coat, creating a thick paste (a roux).
With the heat on medium, whisk in the chicken broth, milk, cream cheese, and rotel. Turn the heat up to medium-high and continue to whisk until the mixture smooths and starts to bubble and thicken. Once it’s bubbling, reduce the heat to low and simmer to reduce for 6-8 minutes.
While it’s simmering, dice the cooked chicken into bite-sized pieces.
Add the cooked spaghetti to the sauce and stir to completely coat. If it’s too thick, add up to 1 cup of reserved pasta water to thin it out to your desired consistency.
Add the chicken and toss to coat then sprinkle the top with mozzarella and parmesan cheese. Bake in the preheated oven for 12-15 minutes, until the cheese is melted and bubbling around the edges, and starting to turn golden brown in a few places on the top.