Special equipment: metal skewers or sturdy wooden skewers (soaked in water for 1 hour)
For the spice mix: Mix together the salt, paprika, cayenne, garlic powder, onion powder, black pepper, oregano and thyme in a small bowl.
For the skewers: Pat the cubes of meat dry and sprinkle generously with the spice mix. Place into large plastic resealable bags and allow to sit in the fridge for 2 to 3 hours.
Prepare a grill for medium-high heat. Thread a chunk of meat on each skewer, followed by a chunk of red pepper, green pepper and onion; repeat this pattern 3 times on each skewer.
Grill the skewers until medium rare, 4 to 7 minutes.