In a heavy-bottom, 12-inch skillet, heat 2 tablespoons (28 g) of the olive oil and 1 tablespoon (14 g) of the butter over medium-high heat until the butter is melted. Add the chopped peppers and onion, and cook, stirring frequently, until softened (about 6 minutes).
Add 1 tablespoon of the fajita seasoning, and stir to combine, then transfer the vegetables to a separate dish and set them aside. Add the remaining 2 tablespoons (28 g) of olive oil, and 1 tablespoon (14 g) of butter to the hot skillet. Once the butter has melted, add the chicken pieces in a single layer. Sprinkle with another 2 teaspoons of fajita seasoning and sauté until browned and cooked in the center (about 4 minutes), stirring only occasionally. Transfer the chicken to a separate dish and set aside.
Add the final tablespoon (14 g) of butter to the hot skillet. Once the butter is melted, add the sweet white rice flour and whisk to combine. Cook for about 1 minute, whisking constantly, until smooth. Continuing to whisk constantly, add the water or chicken stock to the skillet and cook until the mixture thickens (about 2 minutes).
Remove the skillet from the heat, add back the cooked vegetables and chicken and mix to combine. Transfer the mixture to the prepared baking dish, and spread into an even layer. Remove the biscuit quarters from the freezer, and toss with the final teaspoonful of fajita seasoning to coat. Scatter the pieces in an even layer over the top of the chicken mixture in the baking dish. (See Recipe Notes for make-ahead instructions here).
Place in the center of the preheated oven and bake for 20 minutes, or until the biscuits are puffed, golden and baked through. Sprinkle the top with the cheese and return to the oven to bake until the cheese is melted. Remove the dish from the oven, and drizzle with sour cream and top with herbs. Serve immediately.
Notes
To make your own fajita seasoning.Combine 1 teaspoon chili powder (I really like chipotle chili powder), 1 teaspoon kosher salt, 1 teaspoon smoked Spanish paprika, 1 teaspoon granulated sugar, 1/2 teaspoon onion powder, 1 teaspoon garlic powder and 1 teaspoon ground cumin.Make Ahead Option.At this point, the dish can be cooled to room temperature, then covered and refrigerated. When ready to eat, uncover and place right in the preheated oven from the refrigerator and continue with the recipe instructions.