Moroccan lamb and couscous salad

Ingredients

• 2 zucchini (quartered and cut into chunks)
• 2 red peppers (deseeded and cut into chunks)
• 2 yellow peppers (deseeded and cut into chunks)
• 2 red onions (each cut into six wedges)
• 2 tbsp olive oil
• 500 g lamb (trimmed of fat)
• 2 cups couscous
• 2 tbsp cilantro (chopped)
• 1 tbsp fresh flat-leaf parsley (chopped)
• 1 tbsp fresh mint (chopped)
• 8 black olives (pitted, sliced)
• 6 scallions (sliced on the diagonal)
• 1/4 cup lemon juice
• 1 tbsp olive oil
• 3 garlic cloves (crushed)
• 1 tsp ground cumin
• 1 tsp ground coriander
• pinch cayenne pepper
• 7 tbsp tomato juice
• 2 tbsp balsamic vinegar
• 1 tsp chili sauce (or to taste)