To make a tuna stroganoff, you'll first need to prepare the ingredients for the dish. First, heat the olive oil over medium-high heat. Add the onion and cook until softened, about 5 minutes. Then add the garlic and saute until fragrant, 1 minute. Stir in the tomato paste and season with salt and pepper, to taste. Cook the mixture for 2 to 3 minutes, until the sauce thickens. Remove the saucepan from the heat and stir in 2 tablespoons of the sour cream. Season with pepper and salt, and serve.