Heat olive oil in a large skillet over medium heat.

Add the diced onion and minced garlic to the skillet, sautéing until the onion is translucent, about 3-4 minutes.

Add the ground beef to the skillet, breaking it apart with a spatula. Cook until browned, about 5-7 minutes.

Stir in the sliced bell pepper and zucchini, cooking for an additional 3-4 minutes until they start to soften.

Add the cherry tomatoes, dried oregano, ground cumin, paprika, salt, and pepper. Stir well to combine and cook for another 3-4 minutes.

Fold in the fresh spinach and cook until just wilted, about 1-2 minutes.

Remove from heat and squeeze fresh lemon juice over the stir-fry. Mix well.

Serve warm, garnished with feta cheese and fresh parsley if desired.