Bring a large pot of water to a boil. Salt the water lightly and add 12 ounces rotini. Cook according to package instructions, then drain and set the pasta aside.

While the pasta cooks, heat a large nonstick skillet over medium heat. Add 1 pound cubed boneless skinless chicken breasts and the diced small green and red bell peppers. Cook, stirring occasionally, until the chicken is cooked through and the peppers are tender, about 6–8 minutes. (If you prefer crunchier peppers, add the peppers after 2–3 minutes of cooking the chicken.) Transfer the chicken and peppers to a bowl and set aside.

In the same skillet, melt 1/2 cup (4 oz) butter over medium heat. Pour in 2 cups half-and-half and bring to a low simmer. Cook, stirring occasionally, until the mixture reduces and thickens slightly, about 5–8 minutes.

Remove the skillet from the heat. Stir in 3/4 cup (3 oz) shredded Parmesan cheese, 1/2 teaspoon dried oregano, 1/2 teaspoon dried basil, 1/2 teaspoon salt, and 1 teaspoon minced chives or green onions (if using). Stir until the Parmesan is melted and the sauce is smooth.

Return the cooked chicken and peppers to the skillet, add the drained rotini, and toss gently to coat everything evenly with the sauce. Warm briefly over low–medium heat if needed, about 1–2 minutes.

Serve immediately, topping with additional Parmesan if desired.