Start by cooking your whole grain pasta in a large pot until al dente, about 8 to 10 minutes. You will know it is ready when it is tender but still has a slight bite to it. This is key to prevent mushy pasta in the bake. Watch closely, or it could overcook.
Heat olive oil in a Dutch oven over medium heat, add cubed chicken, and let it brown nicely. You will smell the chicken aroma filling the kitchen. This gives flavor to your dish while ensuring the chicken is cooked through. Do not overcrowd the pan; it will steam instead of brown.
Stir in the fresh baby spinach or chopped kale into the pan with the chicken. Cook until wilted and vibrant, which will take just a few minutes. This adds lovely color and nutrition to your bake. Allow enough time for the greens to soften or they might be too tough later.
Sprinkle flour over the chicken and greens, stirring to form a roux. You will notice it thickening as it cooks for about a minute. This step is crucial for achieving a creamy sauce later on. Keep stirring to avoid lumps; nobody likes a gritty sauce!
Gradually whisk in chicken or vegetable stock and evaporated milk until the sauce is smooth. As it thickens, you will see its creamy consistency come together. This is the heart of your pasta bake, so take your time. If it feels too thick too quickly, just add a splash of stock.
Sprinkle in salt, pepper, and optional Italian seasoning, tasting as you go. You will want to get that seasoning right for optimal flavor throughout. It is easy to go overboard, so start with a little and adjust as needed.
Mix in half of the shredded cheese, combining until it is melted and gooey. You will start to feel the creaminess come out. If it is not melting well, your heat might be too low.
Gently fold the cooked pasta into the sauce mixture, making sure every noodle gets coated. It should look creamy and inviting. If it feels too dry, adding a splash of stock will help. Just do not mix too aggressively or you will break the pasta.
Transfer the mixture into a baking dish, topping with remaining cheeses and freshly grated Parmesan. As it bakes in a preheated oven at 375 degrees F (190 degrees C), you will notice the cheese bubbling and becoming golden, which indicates it is almost ready. Make sure the toppings are even—too little cheese could lead to dry spots.
Once it is baked and golden, sprinkle with chopped parsley before serving. The color will really pop against the cheesy goodness. Let it cool slightly so you do not burn your mouth on the first bite.