Heat coconut oil in a large pot over medium heat. Add onion and garlic; cook and stir until onion is translucent, 4 to 5 minutes. Pour in vegetable broth and tomato sauce; bring to a simmer, about 5 minutes. Stir in stew vegetables, corn, and green beans; simmer until tender, 15 to 20 minutes. Season with black pepper and salt.
