In a bowl, combine olive oil, soy sauce, lemon juice, garlic, paprika, cumin, salt, and black pepper. Mix well.

Add the chicken cubes to the marinade, cover, and refrigerate for at least 30 minutes.

If using wooden skewers, soak them in water for 30 minutes to prevent burning.

Thread the marinated chicken and optional vegetables onto skewers.

Preheat the grill to medium-high heat.

Place the skewers on the grill and cook for about 10-15 minutes, turning occasionally, until the chicken is cooked through and has nice grill marks.