Preheat oven to 400F. Remove stem from cabbage and break into bite-size florets. Halve the eggplant and cut into bite-size pieces. Drain the beans, rinse, and pat dry. Halve the red onion and cut into quarters.
In a bowl, mix together olive oil, harissa paste, maple syrup, orange zest, spices, and a pinch of salt. Taste to adjust the seasoning. Grease 2 quarter sheet trays and toss the cabbage and eggplant with half of the harissa mixture on one tray, and toss the beans with red onion on the other tray. Roast in the oven for 30-35 minutes or until fork tender, tossing the vegetables once midway through.
While the vegetables cook, prepare couscous per boxed instructions. Once cooked, toss with 2 tbsp chopped parsley and 1 tbsp butter. Prepare lemon yogurt by mixing together yogurt with lemon zest and juice from ½ lemon.
Remove vegetables from oven, squeeze remaining lemon half over vegetables, toss and serve with couscous and lemon yogurt.
