In a skillet or frying pan, melt butter over medium heat. Add diced onion and cook until onion is translucent and cooked (about 3-5 minutes). Add garlic and cook until fragrant (~1-2 minutes). In a separate saucepan, cook rice according to package instructions.
Slowly sprinkle about 1-2 Tbsp of brown rice flour at a time to the butter mixture in pan, stirring with a whisk. Continue adding 1-2 Tbsp of brown rice flour until the flour is gone. Mixture should be dry and almost look like it's formed a "dough".
Add chicken base to hot water and mix until dissolved to make chicken broth. Slowly add 1-2 TB of milk and chicken broth to the flour mixture at a time, stirring with a whisk until a sauce forms. Do not add too much milk too fast or the sauce will not form and you will have huge pieces of flour in your sauce (gross!)
Let the sauce simmer until it starts to thicken. Add diced chicken to the sauce. Add pepper. Stir the sauce and let simmer until the sauce has thickened to your liking, turning down the heat, if needed.
To assemble, place rice on the bottom, chicken gravy on top, and add toppings as desired. Topping ideas: Olives, cheese, green peas, sliced almonds, steamed broccoli, bell peppers, pineapple, mandarin oranges, shredded coconut, or anything else you might enjoy!