Prepare the Beef: In a large skillet or wok, heat olive oil over medium-high heat. Add the ground beef and cook, breaking it up with a spoon, until browned. Drain off any excess grease.

Bloom the Aromatics: Add the chopped onion to the skillet and cook until softened, about 3-5 minutes. Add the minced garlic, dried oregano, dried basil, and red pepper flakes (if using), and cook for another minute until fragrant.

Incorporate the Vegetables: Stir in the tomato paste and cook for 1 minute. Add the bell pepper and zucchini and cook for 5-7 minutes, or until crisp-tender. Add the halved cherry tomatoes and Kalamata olives and cook for another 2-3 minutes, until the tomatoes begin to soften but still hold their shape.

Finish and Serve: Season with salt and pepper to taste. Stir in the fresh parsley and lemon juice. Remove from heat and sprinkle with crumbled feta cheese. Serve immediately.