Step 1

Preheat oven to 400°F.

Step 2

Heat sun-dried tomato oil in a large cast-iron skillet over medium heat. Add onion and cook, stirring, until beginning to brown, about 4 minutes. Add spinach and garlic; cook, stirring, for 1 minute. Add rice, stirring to coat and break up clumps.

Step 3

Whisk broth, cream cheese, sour cream, cornstarch, mustard, salt and pepper in a measuring cup until smooth. Pour into the skillet and cook, stirring, until bubbling and thickened, 3 to 5 minutes. Remove from heat and stir in chicken, sun-dried tomatoes and 1/2 cup cheese. Sprinkle the remaining 1/2 cup cheese over the top. Bake until the casserole is hot and the cheese has melted, 15 to 20 minutes.