Slice the bell pepper, zucchini, and red onion. Halve the cherry tomatoes and mince the garlic.

In a large skillet, heat the olive oil over medium-high heat. Add the ground beef and cook until browned, about 5-7 minutes.

Add the sliced onion and garlic to the skillet. Sauté for 2-3 minutes until the onion is translucent.

Stir in the bell pepper, zucchini, and cherry tomatoes. Cook for an additional 5-7 minutes until the vegetables are tender.

Sprinkle the oregano, salt, and pepper over the stir-fry. Drizzle with lemon juice and stir well to combine. Serve hot.