Add sesame oil to a medium Dutch oven or ddukbaeggi over medium-low heat. Add gochugaru and stir for about 2 minutes, until it starts to froth.
Add onions, garlic, and zucchini. Stir and cook in gochugaru for about 1 minute, until onions begin to soften. Add gochujang and stir until vegetables are evenly coated. Deglaze the pot with soy sauce and stir. Then, add vegetable broth.
Increase heat and bring the pot to a boil (about 2 minutes). Then reduce heat and allow the pot to simmer for about 15 minutes, until the zucchini is completely tender and the broth infused with their flavor.
Add tofu and cook for about 3 more minutes. Garnish with scallion greens, sesame oil, black pepper, and toasted sesame seeds.