To prepare a spicy tuna rice bowl recipe, you'll first need to prepare the rice. You can use white rice or brown rice, depending on your preference. Heat the oil over medium-high heat. Add the onion and cook until softened, about 5 minutes. Stir in the garlic, ginger, and salt and pepper to taste. Cook, stirring frequently, until the onions are translucent and the ginger is fragrant, 2 to 3 minutes more. Remove the pan from the heat and add the diced tomatoes. Toss to coat the tomatoes with the spice mixture. Serve with sour cream, if desired.