Prepare all the vegetables before beginning. Slice the bell pepper, zucchini, and onion, halve the cherry tomatoes, and mince the garlic.
Heat the olive oil in a large skillet over medium-high heat.
Add the ground beef and break it into smaller pieces with a wooden spoon or spatula.
Cook for 5–7 minutes, stirring occasionally, until the beef is browned and cooked through. If there is a large amount of excess fat, carefully drain some before continuing.
Add the sliced onion and minced garlic.
Cook for 2–3 minutes, stirring frequently, until the onion begins to soften and the garlic is fragrant.
Add the bell pepper and zucchini. Cook for about 4 minutes, stirring occasionally.
Add the halved cherry tomatoes and continue cooking for another 2–3 minutes. The vegetables should be tender but still retain some texture.
Sprinkle the oregano, salt, and black pepper evenly over the Mediterranean Ground Beef Stir-Fry.
Drizzle with fresh lemon juice and toss everything together until evenly combined.
Cook for approximately 1 additional minute, then remove the skillet from the heat.
Taste and adjust the salt, pepper, oregano, or lemon juice if necessary.
Garnish with fresh parsley if desired and serve hot