Preheat oven to 375°F. Grease a 9x13 baking dish and set aside.
Bring a large pot of salted water to a boil. Cook spaghetti until just under al dente according to package directions. Reserve 1 cup of pasta water, then drain.
In a large Dutch oven or heavy-bottomed pot, heat 1 tablespoon butter and olive oil over medium heat.
Add onion, bell pepper, and poblano pepper. Cook for 5-6 minutes until softened.
Add garlic and cook for 30 seconds until fragrant.
Add 3 tablespoons butter and allow it to melt. Sprinkle in flour and whisk continuously for 1 minute.
Slowly whisk in chicken stock until smooth. Add heavy cream and continue whisking.
Reduce heat to low and stir in cream cheese, Velveeta, Rotel, Bayou City All Purpose Seasoning, Bayou City Garlic Pepper, smoked paprika, Cajun seasoning, and black pepper.
Stir until cheeses are completely melted and the sauce is smooth.
Add shredded chicken and stir to combine.
Add cheddar cheese, mozzarella cheese, and parmesan cheese. Stir until melted.
Fold in cooked spaghetti. If needed, add a splash of reserved pasta water to loosen the sauce.
Transfer mixture to prepared baking dish.
Top with remaining cheddar, mozzarella, parmesan, and crushed crackers if using.
Bake for 20-25 minutes until bubbly and golden.
Broil for 1-2 minutes for additional browning if desired.
Garnish with chopped parsley and serve warm.
