1Add 1.5-2lb cubed boneless skinless chicken thighs in a large bowl. Drizzle with 1/2 tbsp olive oil, 2.5 tbsp plain greek yogurt, 2 tbsp tomato paste, juice of 1 large lemon, 6 minced garlic cloves, 1 tbsp oregano, 1 tbsp sweet paprika, 1/3 tsp cinnamon, 1 tsp cumin, & a couple pinches salt + pepper.
2Mix well and marinate for 2-6 hrs, ideally overnight.
3Bring chicken to room temperature for 30 mins and preheat oven to 400F.
4Line a baking tray with parchment paper, and add the chicken without overcrowding. Cut 2 red onions into small wedges and toss around the chicken on the tray. Drizzle with more olive oil & sprinkle with about 1 tbsp sumac over everything.
5Pop into the oven at 400F for 37-40 mins.
6Make the cucumber sauce by mixing 3/4 cup plain greek yogurt, 1 Persian cucumber finely diced, 3 tbsp finely chopped fresh dill, 1 small shallot finely shredded/processed, juice of half a lemon, a couple pinches salt & pepper.
7Remove the sheet pan from the oven, then top with a few dollops of the spread, lots of fresh herbs (parsley, dill, or mint would be great here!), another dusting of sumac, and fresh lemon juice.