Fill a medium pot 3/4 of the way up with salted water; cover and heat to boiling on high. Wash and dry the fresh produce. Medium dice the cucumber(s). Halve the tomatoes. Quarter and deseed the lemon(s). Peel 2 cloves of garlic (or 4 cloves for 4 servings); using a zester or the small side of a box grater, finely grate into a paste. Halve, peel, and thinly slice the onion(s). In a bowl, combine the diced cucumber(s), halved tomatoes, up to half the za'atar, a drizzle of olive oil, and the juice of 2 lemon wedges (or 4 wedges for 4 servings); season with salt and pepper. In a separate bowl, combine the sour cream, the juice of the remaining lemon wedges, and as much of the garlic paste as you'd like. Season with salt and pepper.

Add the couscous to the pot of boiling water. Cook, uncovered, 5 to 7 minutes, or until tender. Turn off the heat. Drain thoroughly and return to the pot; drizzle with olive oil and season with salt and pepper. Stir to combine.

Meanwhile, in a medium nonstick pan (or large for 4 servings), heat a drizzle of olive oil on medium-high until hot. Add the beef and sliced onion(s) in an even layer; break the meat apart with a spoon. Cook, without stirring, 3 to 4 minutes, or until lightly browned. Carefully drain off and discard any excess oil. Add the harissa paste and tomato paste. Season with salt and pepper. Cook, stirring frequently, 1 to 2 minutes, or until thoroughly combined. Carefully add 1/3 cup of water (or 2/3 cup for 4 servings). Cook, stirring occasionally, 1 to 2 minutes, or until slightly thickened and the beef is cooked through. Turn off the heat. Serve the cooked couscous topped with the cooked beef and onion(s), cucumber-tomato salad, and lemon sour cream. Garnish with as much of the remaining za'atar as you'd like. Enjoy!