In a large bowl, whisk together all the ingredients, except for the butter. Set aside.
In a large saucepan of boiling water, blanch the onions for 2 to 3 minutes or until tender. Drain. Cool under cold running water and peel.
Add the onions, meat, mushrooms, and bell peppers to the marinade. Toss to combine. Cover and refrigerate for at least 4 hours or overnight.
Preheat the grill, setting the burners on high. Oil the grate.
Thread the meat alternately with the vegetables onto the skewers.
Grill the skewers over medium heat for about 4 minutes per side or to the desired doneness. Season with salt and pepper.
Meanwhile, in a small saucepan, bring the marinade to a boil. Simmer for about 5 minutes or until syrupy. Remove the thyme and bay leaf. Remove from the heat and whisk in the butter. Adjust the seasoning.
Serve the skewers on a bed of Egg Noodles with Sour Cream (see recipe). Top with the reduced sauce. Sprinkle with the parsley.