In a bowl, mix the vegetable oil, chopped onion, minced garlic, chopped hot peppers, ground cumin, ground paprika, ground coriander, ground turmeric, ground black pepper, and salt.
If using, add the soy sauce for extra flavor.
Add the meat cubes to the marinade and mix well to coat. Cover and refrigerate for at least 1 hour, or overnight for best results.
Preheat your grill or broiler to medium-high heat.
Thread the marinated meat cubes onto the soaked wooden skewers, alternating with pieces of onion or bell peppers if desired.
Place the skewers on the grill or under the broiler.
Grill for about 10-15 minutes, turning occasionally, until the meat is cooked through and has a nice char.
Garnish with fresh cilantro if desired.
Enjoy your meal!