Combine the soy sauce, balsamic vinegar, thyme and olive oil in a large dish.
Dice the vegetables into similarly sized pieces (about 1 inch square) - I cut the tomatoes into eighths, the mushrooms in half, and separated the onion into layers before cutting into inch sized pieces.
Toss the vegetables with the marinade - you can leave the vegetables sitting in the marinade if desired, for up to 24 hours in the fridge, but a quick toss through the marinade will provide plenty of flavour.
Thread the vegetables onto skewers, reserve the leftover marinade.
Heat up the grill/BBQ over a medium heat and let it preheat for a few minutes.
Place the kebabs on the grill and cook for 5-7 minutes before flipping and cooking for another 5-7 minutes. You may need to flip for an extra 5 minutes if your eggplant doesn't feel cooked through.
Place the cooked kebabs on a large plate and drizzle over the leftover marinade.
Serve immediately.