Soak the cashews in just-boiled water for at least 30 minutes (or up to 1 hour). For a quick soak, simmer on the stovetop for about 10 minutes until plump.
Cook the pasta in lightly salted water according to package directions. Reserve ¾ cup pasta water, then drain and set aside.
In a small bowl, combine onion powder, garlic powder, oregano, smoked paprika, thyme, and cayenne (if using) for the spice mix.
Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Add chicken and sprinkle with 1 teaspoon of Cajun seasoning. Cook, turning occasionally, until chicken is fully cooked. Remove and set aside.
Add the remaining 1 tablespoon olive oil to the skillet. Sauté the onion, bell peppers, and garlic for 3–4 minutes until tender. If the pan browns too quickly, add a splash of water and reduce heat slightly.
Stir in the tomato paste and remaining Cajun seasoning. Cook for 1 minute, stirring constantly, until fragrant and tomato paste darkens slightly. Remove from heat.
Drain the soaked cashews and blend with the broth, nutritional yeast, salt, and pepper until smooth and creamy.
Return the skillet to medium-low heat. Add cooked pasta, chicken, and the cashew cream sauce. Stir to combine, scraping up any brown bits from the pan. Simmer 1–2 minutes until the sauce coats the pasta and chicken. Thin the sauce with reserved pasta water as needed to reach desired consistency.
Adjust seasoning with additional salt and pepper if needed. Garnish with fresh parsley and serve warm.
