Combine sausage, scallions, and garlic in a large soup pot over medium-high heat. Cook and stir until sausage is browned and crumbly and garlic and scallions have browned a bit, about 10 minutes. Mix in okra, diced tomatoes, and tomato sauce until well combined.

Reduce heat and simmer for 20 to 25 minutes. Add mushrooms, salt, and pepper; simmer for another 20 to 25 minutes, adding water if mixture begins to dry out.