Heat olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook until softened, about 5 minutes.

Add the minced garlic and cook for 1 minute more, until fragrant.

Add the ground turkey to the pot and cook, breaking it up with a spoon, until browned. Drain off any excess grease.

Stir in the diced tomatoes (undrained), black beans, corn, Rotel (undrained), chicken broth, chili powder, cumin, oregano, and cayenne pepper (if using). Season with salt and pepper to taste.

Bring the soup to a boil, then reduce heat and simmer for at least 15 minutes, or longer for a richer flavor. The longer it simmers, the more the flavors will meld.

Serve hot, topped with shredded cheese, tortilla chips, sour cream or Greek yogurt, and cilantro or green onions, if desired.