Combine the olive oil, balsamic vinegar, garlic, chilli, molasses and salt and pepper in a screw-top jar, shake well to combine.
Place mushrooms into a large bowl and pour over the vinegar mixture. Toss well to combine. Marinate for 1 hour.
BBQ for 5 - 7 minutes turning once only.
A 100 gram serve of mushrooms has more than 3 grams of fibre and virtually no carbohydrate or fat. With only 172 kj per 100g, they're a great daily contribution to the RDI of 35g of fibre without adding too much extra energy.