Combine orange juice, brown sugar, mustard, bourbon and one teaspoon of salt in a medium saucepan. Whisk in cornstarch until smooth. Bring to a boil and cook until glaze has thickened, about 1-2 minutes. Set glaze aside to cool slightly.
Cut the pork loin into 1-inch pieces. Toss the pork loin in half the glaze until coated. Set the other half of the glaze aside for basting.
Slice the peppers into sections large enough to skewer. Cut the purple onion in the eighths.
Toss the peppers, onion and the mushrooms with the olive oil and the remaining teaspoon of salt.
Thread the meat and vegetables onto the skewers – alternating the meat with the vegetables.
Preheat a grill to medium high heat or preheat the broiler and move the oven rack to the top third of the oven. Grill or broil for seven minutes. Turn the kebabs over and baste with the reserved marinade. Grill or broil for an additional seven minutes.
Serve with any remaining glaze for dipping.
Soak wooden skewers in water 30 minutes prior to grilling to prevent the skewers from burning.