Heat the olive oil [ing_1] in a large skillet or Dutch oven over medium-high heat. Add the diced chicken [ing_2] and sausage slices [ing_3]. Cook, stirring occasionally, until the chicken is browned on all sides and cooked through, and the sausage is nicely seared. Remove the cooked meats from the skillet and set aside, leaving any drippings behind.
Add the chopped onion [ing_5] and red bell pepper [ing_6] to the same skillet (add a splash more oil if needed). Cook, stirring, until they start to soften, about 5-7 minutes. Add the minced garlic [ing_7] and Cajun seasoning [ing_4] and cook for another minute until fragrant.
Pour in the chicken broth [ing_9] and scrape the bottom of the pan with a wooden spoon to loosen any browned bits. Bring to a simmer and let it cook for a couple of minutes. Reduce the heat to low, then stir in the heavy cream [ing_10] and the can of diced tomatoes with green chilies [ing_11]. Let the sauce simmer gently for about 5 minutes, stirring often, until it starts to thicken slightly.
While the sauce is simmering, cook the penne pasta [ing_8] according to package directions, but undercoook it by about 2-3 minutes. Drain the pasta well.
Return the cooked chicken [ing_2] and sausage [ing_3] to the skillet with the sauce. Add the drained, slightly undercooked pasta [ing_8] to the skillet. Stir gently to coat everything evenly in the creamy sauce. Taste and add salt [ing_14] and pepper [ing_15] if needed. Remember that the sausage and Cajun seasoning have salt, so start slow!
Preheat your oven to 375°F (190°C). Pour the pasta mixture into a 9x13 inch baking dish. Sprinkle the shredded mozzarella [ing_12] and cheddar cheese [ing_13] evenly over the top.
Bake for 20-25 minutes, or until the sauce is bubbly around the edges and the cheese is melted and golden brown. If you want the cheese extra browned, you can pop it under the broiler for a minute or two at the end, but watch it carefully!
Let the pasta bake rest for 5-10 minutes before serving. Garnish with fresh chopped parsley [ing_16] if you like. Dig in and enjoy!