Heat a large saucepan over medium high heat and add olive oil and diced onion. Cook until softened then add garlic. Stir and allow to heat and become fragrant. Season with salt and pepper.
Add rice and stir, then add the chicken or vegetable stock. Let it come to a boil, then reduce to a simmer, cover and let cook until rice is done. Timing will be dependent on what type of rice you use. Check the package instructions, but it should take between 20-55 minutes. Brown rice generally takes the longest to cook.
Once the rice is cooked, turn off the heat, stir in the fresh oregano. Transfer to a large mixing or serving bowl. Add in the remaining ingredients, stirring to combine everything well. Taste and adjust seasonings if needed.
Top with additional feta and parsley if you’d like, and serve!