Bring a large pot of salted water to a boil. Cook pasta according to package instructions until al dente. Reserve 1/4 cup of pasta water, then drain.
Season chicken cubes with salt and pepper. In a large skillet, heat olive oil over medium-high heat.
Add chicken to the skillet and cook until golden brown and cooked through, approximately 6 to 8 minutes. Remove chicken from the skillet and set aside.
In the same skillet, melt butter over medium heat. Add diced onion and sauté for 3 minutes until translucent. Add minced garlic and cook for 1 minute until fragrant.
Pour in heavy cream and Sriracha sauce. Whisk to combine and bring to a gentle simmer for 3 minutes until the sauce begins to thicken.
Stir in the Parmesan cheese until melted and the sauce is smooth.
Add the cooked pasta and chicken back into the skillet. Toss thoroughly to coat. If the sauce is too thick, stir in the reserved pasta water 1 tablespoon at a time until desired consistency is reached.
Garnish with chopped parsley and serve immediately.