In a mixing bowl, combine chili oil, minced garlic, smoked paprika, onion powder, salt, pepper, and lemon juice to create a flavorful marinade. Add the boneless chicken thighs or breasts, ensuring each piece is well-coated. Cover the bowl and refrigerate for at least 30 minutes to let the flavors meld and infuse into the chicken.

Fill a large pot with water, adding a generous pinch of salt, and bring it to a boil over high heat. Once boiling, add the rotini pasta and cook according to package instructions until al dente, typically 8-10 minutes. Reserve ½ cup of the pasta water, then drain the pasta and set it aside, allowing it to cool slightly while you prepare the rest of the dish.

Preheat a grill pan over medium-high heat until hot, about 5 minutes. Remove the marinated chicken from the refrigerator and place it on the grill, cooking for 4-5 minutes on each side until charred and cooked through, reaching an internal temperature of 165°F. Once done, transfer the chicken to a cutting board to rest before slicing into bite-sized pieces.

In a large saucepan, melt 2 tablespoons of butter and 1 tablespoon of olive oil over medium heat. Add minced garlic, sautéing for about 1 minute until fragrant. Stir in the heavy cream and Cajun seasoning, letting it simmer gently for 3-4 minutes. Gradually whisk in the grated Parmesan cheese until melted and smooth, creating a rich, creamy Cajun Alfredo sauce ready to coat the pasta.

In a separate frying pan, heat 1 tablespoon of olive oil over medium heat. Add the sliced zucchini and bell peppers, seasoning them with salt and pepper. Sauté for about 5-7 minutes, stirring occasionally until the vegetables are slightly charred and tender.

In the saucepan with the Alfredo sauce, add the cooked rotini pasta and toss it gently to coat thoroughly. If the sauce is too thick, gradually stir in the reserved pasta water until you achieve your desired consistency. Plate the creamy pasta, top it with the grilled chicken slices, and arrange the sautéed vegetables alongside. Garnish with fresh parsley or cilantro before serving hot.