In a large bowl, whisk together olive oil, cumin, smoked paprika, coriander, cayenne pepper, garlic powder, salt, and pepper. Add the chicken cubes and toss until they are well coated in the spice mixture. Cover and let marinate in the refrigerator for at least 30 minutes, or overnight for deeper flavor.
Preheat your grill or grill pan to medium-high heat. Ensure the surface is clean and lightly oiled to prevent sticking.
Thread the marinated chicken cubes onto skewers, dividing them evenly.
Place the chicken kebabs on the grill and cook for 7-8 minutes on each side, or until the chicken is fully cooked through and has a nice char on the outside.
While the kebabs are grilling, combine Greek yogurt, grated cucumber, lemon juice, minced garlic, and chopped dill in a bowl. Season with salt and pepper to taste. Stir until well combined and refrigerate until ready to serve.
Once the chicken is cooked, remove from the grill and let rest for a couple of minutes. Serve the kebabs with the yogurt and cucumber sauce on the side.