Heat the oil in a large pan on medium-high heat. Add the bell pepper and cherry tomatoes and saute for 4 to 5 minutes, until the tomatoes are blistered and saucy. Add the garlic and stir another minute.

Add the spinach and white parts of the green onion. Stir for another 2 to 3 minutes, until the spinach has wilted. Remove these veggies to a plate.

Add the ground beef, oregano, salt, and black pepper to the pan, and use a spatula to break up the meat. Cook the ground beef until it's browned, then drain off any excess grease.

Transfer the veggies back to the pan, add the green parts of the green onion, and stir until warmed through. Garnish with crumbled feta before serving.