Cut the green peppers first in halves and then in thirds the long way. Remove the seeds and cut each piece across. You now have 12 squares of green pepper.
Peel the yellow onions and cut in half across the middle. Cut each piece in quarters. Peel the layers so that you have 6 pieces about the same size as the green pepper squares.
Place the green peppers and onions in a large mixing bowl along with the lamb. Make a sauce of the olive oil, oregano, mint (more if fresh mint), garlic and soy sauce. Mix well, and pour over the meat and vegetables. Mix well again and let sit for 3 hours.
Arrange on skewers in this order: onion, meat, green pepper, meat, onion, meat, green pepper, meat. End with an onion. Grill until lightly browned on all sides, approximately 15 minutes (don't overcook).
Notes: These can also be broiled in the oven. You can substitute good beef cubes for the lamb and it still is one of the best!