Heat sunflower oil in a large pot over medium-high heat. Saute onions in hot oil until golden, 5 to 10 minutes. Add rice to onions and cook until fragrant, about 1 minute.
Stir water, pumpkin, beans, cranberries, and vegetable bouillon into rice mixture. Bring mixture to a boil, reduce heat to low, and simmer for 5 minutes, stirring occasionally. Pour rice mixture into a large baking dish and cover with aluminum foil.
Bake in the preheated oven until water is absorbed and rice is tender, about 45 minutes. Stir chives into rice mixture and season with salt and pepper.