Halloumi and sweet potato skewers with lentil salad

Ingredients

• 2 medium sweet potatoes
• 1 bunch green onions
• 250 g Halloumi cheese , cut into 1 1/2 x 1/4-in. slices
• 1/4 cup olive oil , divided
• 2 tbsp red wine vinegar
• 1 tsp honey
• 2 tsp sumac , divided
• Pinch of salt
• 1/2 tsp pepper
• 1 540-mL can lentils , drained and rinsed
• 1/2 head radicchio , finely shredded (3 cups)
• 2 cups parsley leaves