Heat olive oil in wide skillet over medium. Cook onions slowly 5-6 minutes, stirring often, until translucent and golden at edges.
Add garlic and stir 30 seconds until fragrant.
Crumble in beef and season with salt, pepper, cumin, paprika, oregano, and red pepper flakes. Spread in even layer and cook undisturbed 1-2 minutes, then break apart. Cook 6 minutes total until deeply browned.
Fold in bell pepper and zucchini. Cook 5 minutes, stirring occasionally, until softened but still slightly crisp.
Add cherry tomatoes and olives. Stir gently and cook 2-3 minutes until tomatoes release juices.
Remove from heat. Toss in parsley and squeeze lemon juice over top. Stir to combine.
Transfer to serving dishes. Top with feta, pine nuts, and sumac if using.
Notes
Use 85% lean or higher beef for balanced flavor without excess grease.
Small zucchini have best texture with fewer seeds.