Heat the oil in a deep saucepan. Add the onion and fry until translucent, then add the garlic and fry until light golden brown. Add the cumin seeds and fry until they begin to pop and release their aroma, about 30 seconds.
Mix in the calabaza, squash, or pumpkin and brown sugar and sauté for 1 to 2 minutes. Cover the pot, lower the heat to medium-low, and cook for about 10 minutes.
Remove the lid and mix well. The squash should have released some liquid. If the pot is dry, add about ¼ cup of water. Stir in the green seasoning, tomato, salt, and black pepper. Cover the pot and simmer for about 15 to 20 minutes, or until the pumpkin/squash can be mashed easily.
Remove the pot from the heat, mash the pumpkin/squash until smooth, and return it to the heat. Cook for 1 to 2 minutes. Serve as a side dish with rice or roti.