Mediterranean Shish Kebab with Grainy Mustard Aioli Sauce

Ingredients

• 4 boneless, skinless chicken breasts, chopped
• 1 red pepper, cubed
• 1 green pepper, cubed
• 8 mushrooms
• 1/4 cup ketchup
• 1/4 cup plain yogurt
• 1/4 cup vegetable oil
• 1 lemon, juiced
• 1 tsp allspice
• 1/4 cup cider vinegar
• salt, to taste
• pepper, to taste
• 2 cloves garlic, minced
• 1/4 cup mayonnaise
• 2 tsp grainy mustard