In a large pot or Dutch oven over medium-high heat, warm the olive oil and melt the butter. Add the chopped onion and sauté for 3 to 4 minutes until softened and translucent.

Stir in the garlic, Italian seasoning, sun-dried tomatoes, lemon juice, Dijon mustard, and orzo. Cook for 2 to 3 minutes, stirring often, so the orzo absorbs the flavors.

Pour in the chicken broth and heavy cream. Bring the mixture to a gentle bubble, then reduce the heat to medium or medium-low. Cook uncovered for about 10 minutes, stirring fairly often, until the orzo is tender and the liquid has thickened slightly. The liquid should simmer steadily but not boil vigorously.

Remove the pot from the heat. Stir in the Parmesan cheese, spinach, and basil. Cover the pot and let it sit for a few minutes until the spinach wilts and the sauce reaches your desired consistency. The orzo will continue to absorb liquid as it rests. Season with salt and pepper to taste before serving.