Heat a large pot over medium heat.
Add chopped onions and sauté until translucent.
Stir in minced garlic and cook for another minute.
Add diced tomatoes and cook for 5 minutes.
Pour in vegetable broth and bring to a simmer.
Add corn and diced bell pepper.
Season with cumin, chili powder, salt, and pepper.
Simmer for 20 minutes, stirring occasionally.
Remove from heat and blend slightly for a smoother texture, if desired.
Serve hot, garnished with fresh cilantro and avocado slices.