Start by soaking 6-8 bamboo skewers in water for at least 20 minutes before using. This will prevent burning while grilling the veggies.
Prepare the veggies. Peel the onions and garlic, wipe the mushrooms with a wet sponge, remove the seeds from the bell peppers. Cut all the veggies (except the garlic) into similar sizes, around 1 - 1 1/2 inches (3-5 cm). Cut the onion in half, then each half into 3. Cut the zucchini in half lengthwise, then each half in two lengthwise. Then chop into 1/2 inch (1.5 cm) pieces. Cut the peppers in half and remove the seeds. Cut each half into 3-4 pieces lengthwise and then 1 inch pieces. Make sure your veggies are of similar size, more or less.
Start arranging the veggie pieces on the skewers. Alternate the colors so they look appealing. Do not squeeze the veggie pieces into each other, they should lightly touch. This will ensure even cooking and no raw patches in between. Arrange the skewers on a baking sheet covered with baking paper.
Heat up the grill or place a grilling pan on medium or medium-high heat. Once the grill/pan is hot, add the well oiled veggie skewers.
Prepare the garlic herb marinade. Mix all of the ingredients: olive oil, pressed garlic, lemon zest, lemon juice, honey, parsley, oregano, salt, and pepper.
Brush the veggie skewers with the marinade. Use tongs to place the skewers onto the grill.
Let the veggies cook for 3-5 minutes on one side before turning. This will help develop those nice char marks. Repeat these process 3-4 more times. You can also brush the veggies with more marinade while cooking. As the veggies start to cook and become more tender, decrease the turning time to 2-3 minutes for each side.
Once the veggies are cooked, serve and enjoy!