Step 1

Combine tomatoes, yogurt, garlic, and ginger in a blender and process until smooth.

Step 2

Heat oil in a large frying pan over medium heat. Add onion and fry until soft, 3 to 4 minutes, stirring constantly. Stir in curry paste and fry until fragrant, 1 minute more, stirring once or twice. Add the tomato mixture and chicken to the pan and mix together. Season with salt and pepper. Remove pan from heat.

Step 3

Mix water and flour together in a bowl. Stir into the chicken mixture in the frying pan. Return pan to the heat and bring to a boil, stirring constantly, about 5 minutes. Reduce heat to low, cover, and cook until thickened, about 15 minutes more. Sprinkle with cilantro and serve immediately.