Begin by prepping all ingredients, ensuring they are organized and ready for use according to the ingredient list. Cook the penne pasta according to package instructions, drain, and set aside to keep warm.

While the pasta is cooking, season the chicken pieces with salt, black pepper, granulated garlic, granulated onion, and about ¼ cup of the flour. Toss to coat evenly.

Heat a large, heavy-bottomed pan or Dutch oven over medium-high heat. Add approximately 4 tablespoons of olive oil. Once the oil is hot, add the chicken in batches to avoid overcrowding, browning each batch for 4-6 minutes. Remove the chicken from the pan and set it aside. Repeat with the remaining chicken.

In the same pan, add more olive oil if necessary and sauté the sliced mushrooms, seasoning them with salt and pepper. Cook until the mushrooms are golden brown, about 4-5 minutes, then remove them from the pan and set aside with the chicken.

Reduce the heat to medium-low and add the butter to the pan. Once the butter melts, stir in the garlic and cook until fragrant. Add the remaining flour to create a roux, stirring for 30 seconds to 1 minute to remove any raw flour taste.

Gradually whisk in the chicken stock and let the sauce simmer gently for a few minutes until it thickens slightly.

Stir in the Dijon mustard, Italian seasoning, and half-and-half, mixing well.

Add the asparagus and let it simmer gently in the sauce until crisp-tender, checking the seasoning and adjusting salt and pepper as needed.

Return the chicken, mushrooms, and sun-dried tomatoes to the pan, stirring to combine. Let the sauce simmer for another few minutes.