Heat olive oil in a large skillet over medium heat.
Add onion and sauté for 4-5 minutes, until softened. Add garlic and sauté another 30 seconds.
Stir in curry powder, diced tomatoes, and chicken broth. Season with salt, pepper and cayenne, if using.
Bring to a low simmer and cook for 2-3 minutes, until slightly thickened.
Stir in chicken until warmed through, 1-2 more minutes.
Turn off the heat and stir in the Greek yogurt until just combined.
Serve hot with fresh chopped parsley or cilantro and chopped peanuts.
