Dip the tomatoes in hot water for 15 minutes. Cover with a plate. After 15 minutes, peel off their skin and take out the seedy part from inside.
Heat a saucepan over medium heat. Add the bottle gourd, carrot, potato, bell pepper, and 1½ cups of water. Cover the pot and let the vegetables cook for 15 minutes.
Add these vegetables and water to a blender, along with the peeled and de-seeded tomatoes and rosemary. Blend until smooth.