Heat the olive oil in a large skillet over medium heat until shimmering. Add the diced onions and cook for 4-5 minutes over medium-low heat, stirring frequently, until translucent and just starting to get golden edges. Add the minced garlic and grated ginger, stirring constantly for about 30 seconds until fragrant.

Crumble the ground beef into the skillet and immediately season with salt, black pepper, cumin, smoked paprika, oregano, and red pepper flakes if using. Spread the meat in an even layer and let it sit undisturbed for 2 minutes to develop a brown crust. Break it up with a wooden spoon and continue cooking for 6-8 minutes, stirring occasionally, until deeply browned with no pink remaining.

Add the diced bell pepper and zucchini to the skillet, stirring to combine with the beef. Cook over medium heat for 5 minutes until the vegetables soften while keeping some crunch. Fold in the cherry tomatoes and Kalamata olives, stirring gently. Cook for 2-3 minutes until the tomatoes just begin to soften and release their juices.

Remove the skillet from heat and immediately toss in the fresh chopped parsley. Squeeze the lemon juice over the entire dish and give everything a final stir. Top with crumbled feta cheese, toasted pine nuts, and a light sprinkle of sumac if using. Serve immediately while hot.