Begin by boiling a large pot of salted water over high heat. Add the penne pasta and cook according to package directions, usually about 8-10 minutes, until al dente. Stir occasionally to prevent sticking. Once cooked, drain the pasta and set it aside, keeping a small amount of the pasta water to adjust the sauce's consistency later if needed.

In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Add the diced onion and a mix of colorful bell peppers. Sauté for 1-2 minutes, stirring frequently until they begin to soften and the onions turn translucent. Then, add minced garlic and cook for an additional minute, allowing the garlic to become fragrant without burning.

Dice the boneless, skinless chicken breast into bite-sized pieces. Add the chicken to the skillet with the sautéed vegetables and sprinkle with fajita seasoning. Cook for 5-7 minutes, stirring frequently, until the chicken is no longer pink in the center and reaches an internal temperature of 165°F (75°C).

Once the chicken is properly cooked, reduce the heat to medium-low and stir in the cooked penne pasta, Ro-tel diced tomatoes and green chilies, and heavy cream. Mix thoroughly, allowing the creamy sauce to coat all the ingredients evenly. If the mixture feels too thick, add a splash of the reserved pasta water.

Stir in the shredded Monterey Jack cheese until it melts into the sauce and creates a creamy blanket over the pasta, taking about 2-3 minutes. Ensure everything is well combined and heated through.

Remove the skillet from the heat and garnish your Chicken Fajita Pasta with fresh cilantro, chopped green onions, or jalapeños if desired. Serve immediately in bowls.