Heat up the dutch oven over medium heat. Add 1 teaspoon olive oil, onion, and garlic. Saute until translucent, then add ground beef – cook until browned. Remove from heat and drain excess fat.
In another pot, allow water to a boil. Add farro and a touch of salt, and boil for 8 to 10 minutes. Drain and set to the side.
Return the dutch oven to heat, add canned tomatoes, tomato sauce, and mushrooms saute for about 5 minutes. Add ground beef mixture and bring to simmer. Mix in cooked farro and reduce variety for 10 minutes.
Scoop beef mixture into halved peppers and sprinkle with crumbled feta. Cover and cook for additional 10 minutes. Remove from heat, allow to rest for 3 minutes and serve.