In a large skillet, heat olive oil over medium-high heat. Add the diced red bell pepper and cherry tomatoes. Cook for 4–5 minutes, until the tomatoes are blistered and begin to release their juices. Stir in the minced garlic and cook for another minute until fragrant.

Add the spinach and the white parts of the green onion. Stir frequently. The spinach will shrink quickly—this should take about 2–3 minutes. Once wilted, transfer the vegetable mixture to a plate and set aside.

In the same skillet, add the ground beef, dried oregano, salt, and pepper. Break it apart with a spatula and cook until browned and fully cooked. Drain excess grease if needed.

Return the cooked veggies to the skillet and add the green parts of the green onion. Stir until everything is warmed through. Remove from heat and top with crumbled feta, if using.